Forming three-dimensional (3d) electronic parts

ABSTRACT

In an example method for forming three-dimensional (3D) printed electronic parts, a build material is applied. An electronic agent is selectively applied in a plurality of passes on a portion of the build material. A fusing agent is also selectively applied on the portion of the build material. The build material is exposed to radiation in a plurality of heating events. During at least one of the plurality of heating events, the portion of the build material in contact with the fusing agent fuses to form a region of a layer. The region of the layer exhibits an electronic property. An order of the plurality of passes, the selective application of the fusing agent, and the plurality of heating events is controlled to control a mechanical property of the layer and the electronic property of the region.

BACKGROUND

Three-dimensional (3D) printing may be an additive printing process usedto make three-dimensional solid parts from a digital model. 3D printingis often used in rapid product prototyping, mold generation, mold mastergeneration, and short run manufacturing. Some 3D printing techniques areconsidered additive processes because they involve the application ofsuccessive layers of material. This is unlike traditional machiningprocesses, which often rely upon the removal of material to create thefinal part. 3D printing often requires curing or fusing of the buildingmaterial, which for some materials may be accomplished using melting orsintering, and for other materials may be accomplished using digitallight projection technology

BRIEF DESCRIPTION OF THE DRAWINGS

Features of examples of the present disclosure will become apparent byreference to the following detailed description and drawings, in whichlike reference numerals correspond to similar, though perhaps notidentical, components. For the sake of brevity, reference numerals orfeatures having a previously described function may or may not bedescribed in connection with other drawings in which they appear.

FIG. 1 is a schematic view of an example 3D printing system;

FIGS. 2A through 2C are schematic views depicting one example of amethod for forming a 3D printed electronic part;

FIGS. 3A through 3D are schematic views depicting another example of amethod for forming a 3D printed electronic parts, where the methodutilizes an electronic agent, a fusing agent, and a detailing agent;

FIGS. 3E, 3A, 3F and 3G are schematic views depicting still anotherexample of a method for forming a 3D printed electronic part, where themethod utilizes an activating agent, an electronic agent, a fusingagent, and a detailing agent;

FIGS. 4A through 4D are schematic views depicting yet another example ofa method for forming a 3D printed electronic part, where the methodutilizes an activating agent, an electronic agent, a fusing agent, and adetailing agent;

FIGS. 5A, 5B and 5C respectively depict A) an image from astereolithography (.stl) file illustrating a design for a load cell, B)a photograph of the load cell formed via an example of the methoddisclosed herein in accordance with the design in FIGS. 5A, and C) anx-ray image of the example load cell of FIG. 5B; and

FIG. 6 is a flow diagram illustrating an example of a method for formingthree-dimensional (3D) printed electronic parts.

DETAILED DESCRIPTION

Building and/or embedding electronics (e.g., a conductive element) onand/or within a dense part may require multiple steps to assembleseveral different components. For example, three-dimensional printingtechniques, such as extrusion or additive manufacturing, have been usedto create the dense part, and then other techniques, such aselectroplating or the application of conducting materials, have beenused to create the electronics. Many of the materials used to create theelectronics require specific activation procedures, which may utilizespecialized (e.g., proprietary, expensive, etc.) equipment, such asannealing equipment.

Examples of the three-dimensional (3D) printing method disclosed hereinutilize multi jet fusion (MJF) to form a region of a layer that exhibitsan electronic property. During MJF, an entire layer or several layers ofa build material (also referred to as build material particles) is/areexposed to electromagnetic radiation, but a selected region (in someinstances less than the entire layer(s)) of the build material is fusedand hardened to become a layer or several layers of a 3D object/part. Inthe examples disclosed herein, an electronic agent, in combination withan activating agent and/or a fusing agent, is selectively deposited incontact with the selected region of the build material. The agents arecapable of penetrating into the layer of the build material andspreading onto the exterior surface of the build material. The activatedelectronic agent and/or the fusing agent is capable of absorbingelectromagnetic radiation and converting the absorbed radiation tothermal energy, which in turn melts or sinters the build material thatis in contact with the activated electronic agent and/or the fusingagent. This causes the build material to fuse, bind, cure, etc. to formthe layer of the 3D object/part.

The examples of the method disclosed herein utilize multiple printingpasses and multiple heating events, which are controlled in order toobtain parts that exhibit suitable electronic properties (e.g.,conductivity or insulation) and mechanical strength, as well as anaesthetically pleasing surface finish. The multi-printing pass andmulti-heating event approach manages thermal distribution throughout theprocess. Managing thermal distribution can ensure that a desirableelectronic property (such as conductivity) is obtained, and is notdeleteriously affected as a result of overly strong fusing conditions orweak fusing conditions. For example, excessive fusing can cause buildmaterial flow which can in turn cause brittle electronic portions tobreak apart, which could diminish the conductivity. The multi-printingpass and multi-heating event approach also includes enough heatingevents throughout the process so that the resulting part is mechanicallystrong (e.g., exhibits at least 80% of the bulk material properties), ifdesired.

Some examples of the method disclosed herein also utilize controlledcooling. Controlled cooling keeps the build material from experiencinguncontrolled temperature build up within the regions patterned with theelectronic agent and/or fusing agent, which can lead to melt down of theparts and/or thermal bleed. During thermal bleed, unpatterned regions ofthe build material proximate to the patterned regions unintentionallyfuse due to heat spreading from the patterned regions to the unpatternedregions. Moreover, if the build material reaches a full melt, it may bemore susceptible to curling if the temperature subsequently drops toofar below the recrystallization temperature. By heating and cooling thebuild material several times throughout the process, the build materialcan effectively fuse without ever becoming too cool (e.g., less than 20degrees below the recrystallization temperature) and without overheating(e.g., more than 30 degrees over the melting point). The methodsdisclosed herein enable the build material to be in a controlled,sintered state (i.e., fused, but below that of a low viscosity fullmelt), which leads to well-formed parts.

Generally, the methods disclosed herein include determining an amount ofan electronic agent that corresponds to the desired electronic property,adjusting the processing conditions (e.g., how much of a fusing agent toapply) to achieve the desired fusing temperature in the region(s) of the3D part that is/are to exhibit the desired electronic property,determining the amount of fusing agent that corresponds to achieving thedesired fusing temperature for the region(s) that is/are not to exhibitthe desired electronic property, and if applicable, applying additionalfusing agent to achieve the desired aesthetics and a detailing agent toachieving the desired fusing temperature. In some examples, adjustingthe processing conditions may involve lowering the amount of fusingagent to a level that enables the rest of the part to be processed withthe processing conditions for the electronic feature/component. In theseexamples, the fusing agent may not achieve a desirable color, and thusadditional fusing agent could be added with detailing agent to achievethe desirable color and to not over fuse the part.

Referring now to FIG. 1, an example of a 3D printing system 10 isdepicted. It is to be understood that the 3D printing system 10 mayinclude additional components and that some of the components describedherein may be removed and/or modified. Furthermore, components of the 3Dprinting system 10 depicted in FIG. 1 may not be drawn to scale andthus, the 3D printing system 10 may have a different size and/orconfiguration other than as shown therein.

The printing system 10 includes a build area platform 12, a buildmaterial supply 14 containing build material 16, and a build materialdistributor 18.

The build area platform 12 receives the build material 16 from the buildmaterial supply 14. The build area platform 12 may be integrated withthe printing system 10 or may be a component that is separatelyinsertable into the printing system 10. For example, the build areaplatform 12 may be a module that is available separately from theprinting system 10. The build material platform 12 that is shown is alsoone example, and could be replaced with another support member, such asa platen, a fabrication/print bed, a glass plate, or another buildsurface.

The build area platform 12 may be moved in a direction as denoted by thearrow 20, e.g., along the z-axis, so that build material 16 may bedelivered to the platform 12 or to a previously formed 3D part layer(i.e., fused build material). In an example, when the build material 16is to be delivered, the build area platform 12 may be programmed toadvance (e.g., downward) enough so that the build material distributor18 can push the build material 16 onto the platform 12 to form a layerof the build material 16 thereon. The build area platform 12 may also bereturned to its original position, for example, when a new part is to bebuilt.

The build material supply 14 may be a container, bed, or other surfacethat is to position the build material 16 between the build materialdistributor 18 and the build area platform 12. In some examples, thebuild material supply 14 may include a surface upon which the buildmaterial 16 may be supplied, for instance, from a build material source(not shown) located above the build material supply 14. Examples of thebuild material source may include a hopper, an auger conveyer, or thelike. Additionally, or alternatively, the build material supply 14 mayinclude a mechanism (e.g., a delivery piston) to provide, e.g., move,the build material 16 from a storage location to a position to be spreadonto the build area platform 12 or onto a previously formed 3D partlayer.

The build material distributor 18 may be moved in a direction as denotedby the arrow 22, e.g., along the y-axis, over the build material supply14 and across the build area platform 12 to spread a layer of the buildmaterial 16 over the build area platform 12. The build materialdistributor 18 may also be returned to a position adjacent to the buildmaterial supply 14 following the spreading of the build material 16. Thebuild material distributor 18 may be a blade (e.g., a doctor blade), aroller, a combination of a roller and a blade, and/or any other devicecapable of spreading the build material 16 over the build area platform12. For instance, the build material distributor 18 may be acounter-rotating roller.

As shown in FIG. 1, the printing system 10 also includes an inkjetapplicator (shown as 28A, 28B, 28C, 28D in FIG. 1) for dispensing one ormore of an electronic agent 30, a fusing agent 32, a detailing agent 34,and an activating agent 36. In one example, the system 10 includes arespective inkjet applicator 28A, 28B, 28C, 28D for each of the agents30, 32, 34, 36 being used in the method. In this example, one applicator28A, 28B, 28C, 28D contains a supply of one of the agents 30, 32, 34,36, as well as fluid slots and fluidics for dispensing the agent 30, 32,34, 36. As examples, each applicator 28A, 28B, 28C, 28D may be a thermalinkjet printhead or print bar, a piezoelectric printhead or print bar,or a continuous inkjet printhead or print bar. In another example, thesystem 10 includes one applicator 28A, 28B, 28C or 28D for all of theagents 30, 32, 34, 36 being used in the method. In this example, theapplicator 28A, 28B, 28C or 28D may be a single printhead or print bar,which includes a separate fluid slot and fluidics for each of the agents30, 32, 34, 36 that is to be dispensed from the applicator. As such,while multiple inkjet applicators 28A, 28B, 28C, 28D are shown in FIG.1, it is to be understood that a single inkjet applicator 28A, 28B, 28Cor 28D may be used.

The inkjet applicator(s) 28A, 28B, 28C, 28D may be scanned across thebuild area platform 12 in the direction indicated by the arrow 38, e.g.,along the y-axis. The inkjet applicator(s) 28A, 28B, 28C, 28D may extenda width of the build area platform 12. The inkjet applicator(s) 28A,28B, 28C, 28D may also be scanned along the x-axis, for instance, inconfigurations in which the inkjet applicator(s) 28A, 28B, 28C, 28Ddoes/do not span the width of the build area platform 12 to enable theinkjet applicator(s) 28A, 28B, 28C, 28D to deposit the agents over alarge area of a layer of build material 16. The inkjet applicator(s)28A, 28B, 28C, 28D may thus be attached to a moving XY stage or atranslational carriage 40 that moves the inkjet applicator(s) 28A, 28B,28C, 28D adjacent to the build area platform 12 in order to deposit theagents 30, 32, 34, 36 in predetermined areas of a layer of the buildmaterial 16 that has been formed on the build area platform 12 inaccordance with the method(s) disclosed herein. The inkjet applicator(s)28A, 28B, 28C, 28D may include a plurality of nozzles (not shown)through which the agent(s) 30, 32, 34, 36 is to be ejected.

Each of these physical elements may be operatively connected to acontroller 42 of the printing system 10. The controller 42 may controlthe operations of the build area platform 12, the build material supply14, the build material distributor 18, and the applicator(s) 28A, 28B,28C, 28D. As an example, the controller 42 may control actuators (notshown) to control various operations of the 3D printing system 10components. The controller 42 may be a computing device, asemiconductor-based microprocessor, a central processing unit (CPU), anapplication specific integrated circuit (ASIC), and/or another hardwaredevice. Although not shown, the controller 42 may be connected to the 3Dprinting system 10 components via communication lines.

The controller 42 manipulates and transforms data, which may berepresented as physical (electronic) quantities within the printer'sregisters and memories, in order to control the physical elements tocreate the 3D part. As such, the controller 42 is depicted as being incommunication with a data store 44. The data store 44 may include datapertaining to a 3D part to be printed by the 3D printing system 10. Thedata for the selective delivery/application of the build material 16,the fusing agent 32, the electronic agent 30, etc. may be derived from amodel of the 3D part to be formed. For instance, the data may includethe order in which the agents 30, 32, 34, 36 are to be printed and thelocations on each layer of build material 16 that the agents 30, 32, 34,36 are to be deposited. In one example, the controller 42 may use thedata to control the inkjet applicator(s) 28A, 28B, 28C, 28D toselectively apply the electronic agent 30 and the fusing agent 32 sothat several applications of the electronic agent 30 occur prior to theapplication of the fusing agent 32. In another example, the controller42 may use the data to control the inkjet applicator(s) 28A, 28B, 28C,28D to selectively apply the activating agent 36 before the electronicagent 30, to apply the electronic agent 30 at a maximum loading inseveral passes, to apply the detailing agent 34 in specific locations tocontrol the temperature of the build material 16, and to apply thefusing agent 32 at the end of the printing process. The data store 44may also include machine readable instructions (stored on anon-transitory computer readable medium) that are to cause thecontroller 42 to control the amount of build material 16 that issupplied by the build material supply 14, the movement of the build areaplatform 12, the movement of the build material distributor 18, themovement of the inkjet applicator(s) 28A, 28B, 28C, 28D, etc.

As shown in FIG. 1, the printing system 10 may also include a radiationsource 46, 46′. The radiation source 46, 46′ may be used to expose thebuild area platform 12 (and any build material 16 and/or agent(s) 30,32, 34, 36 thereon) to electromagnetic radiation that ultimately fusesthe build material 16 in contact with the fusing agent 32 (or anelectronic agent 30′ (FIGS. 4A-4D) which includes a radiation absorber)and/or sinters a component of the electronic agent 30.

The radiation source 46, 46′ may be any suitable fusing lamp, examplesof which include commercially available infrared (IR) lamps, ultraviolet(UV) lamps, flash lamps, and halogen lamps. Other examples of theradiation source 46, 46′ may include microwave radiation sources, xenonpulse lamps, IR lasers, etc. As depicted in FIG. 1, the radiation source46, 46′ may be a stationary lamp 46′ or a moving lamp 46. The stationarylamp 46′ may be in a fixed position relative to the build area platform12, and may be turned on when radiation exposure is desired and off whenradiation exposure is not desired. The moving lamp(s) 46 can be mountedon a track (e.g., translational carriage 40) to move across the buildarea platform 12 in a direction as denoted by the arrow 22, e.g., alongthe y-axis. This allows for printing and heating in a single pass. Suchlamps 46 can make multiple passes over the build area platform 12depending on the amount of exposure utilized in the method(s) disclosedherein. In the example shown in FIG. 1, the lamps 46 are mounted atopposite ends of the inkjet applicator(s) 28A, 28B, 28C, 28D so thatheat can be applied to the build material 16 immediately before theagent(s) 30, 32, 34, 36 are deposited and/or immediately after theagent(s) 30, 32, 34, 36 are deposited, depending on the movement of thetranslational carriage 40. In an example, the moving lamp 46 at the leftside of the translational carriage may be a leading lamp and the movinglamp 46 at the right side of the translational carriage may be atrailing lamp.

The radiation source 46, 46′ can be configured to irradiate the entirebuild area platform 12 with a substantially uniform amount of energy.This can selectively fuse the printed portions with fusing agent 32and/or sinter the printed portions with electronic agent 30, whileleaving the unprinted portions of the build material 16 below themelting or softening point.

In one example, the radiation source 46, 46′ can be matched with anabsorber in the fusing agent 32 (or the electronic/fusing agent 30′) sothat the radiation source 46, 46′ emits wavelengths of light that matchthe peak absorption wavelengths of the fusing agent 32 (or theelectronic/fusing agent 30′). A fusing agent 32 with a narrow peak at aparticular near-infrared wavelength can be used with a fusing lamp thatemits a narrow range of wavelengths at approximately the peak wavelengthof the fusing agent 32. Similarly, a fusing agent 32 that absorbs abroad range of near-infrared wavelengths can be used with a fusing lampthat emits a broad range of wavelengths. Matching the fusing agent 32(or the electronic/fusing agent 30′) and the radiation source 46, 46′ inthis way can increase the efficiency of coalescing the build material 16with the fusing agent 32 (or the electronic/fusing agent 30′) printedthereon, while the unprinted build material 16 particles do not absorbas much radiation and remain at a lower temperature.

In the example methods disclosed herein, radiation exposure takes placein multiple passes. Radiation exposure may take place to preheat thebuild material 16, to sinter the electronic agent 30, and/or to fuse thebuild material 16 in contact with the fusing agent 32 (or theelectronic/fusing agent 30′). Depending, at least in part, on the amountof the electronic agent 30, fusing agent 32 and/or detailing agent 34present in the build material 16, the absorbance of the radiationabsorber, the preheat temperature, the radiation source power, and themelting or softening point of the build material 16, an appropriateamount of irradiation can be supplied from the radiation source 46, 46′.When the moving lamps 46 are used, the carriage 40 speed and the lengthof the lamp(s) may also affect the irradiation time. In some examples,the radiation source 46, 46′ can irradiate each layer of build materialfrom about 0.025 seconds (25 milliseconds) to about 1 second per heatingevent. This time range may be suitable, for example, when the carriagepass speed ranges from about 4 inches per second to about 40 inches persecond and the radiation source 46 ranges from about 1 inch to about 4inches in length. In other examples when a lower power lamp is used, theheating event time may be up to 10 seconds. In still other examples whena higher power lamp is used, the heating event time may be down to 1microsecond.

FIG. 1 also illustrates layers 48 of build material 16 on the build areaplatform 12 and a three-dimensional (3D) part 50 formed from some of thebuild material 16 in the layers 48. In some of the examples disclosedherein, the 3D part 50 includes a conductive region 52 and an insulatingregion 54. The 3D part 50 is made up of several fused layers, and eachlayer may include conduction region(s) and/or insulating region(s)depending upon the 3D part 50 that is being formed. Examples of themethods for forming the three-dimensional part 50, including theconductive region 52 and the insulating region 54 will be describedfurther in reference to FIGS. 2A-2C, 3A-3G, and 4A-4D.

One example of the method is shown in FIGS. 2A through 2C. This exampleinvolves the formation of a fused layer 56 (FIG. 2C), which forms atleast part of the conductive region 52 in the final 3D part 50.

The method involves applying the build material 16. While not shown,applying the build material 16 may involve the build material supply 14supplying the build material 16 into a position so that they are readyto be spread onto the build area platform 12. The build materialdistributor 18 may spread the supplied build material 16 onto the buildarea platform 12. The controller 42 may execute control build materialsupply instructions to control the build material supply 14 toappropriately position the build material 16, and may execute controlspreader instructions to control the build material distributor 18 tospread the supplied build material 16 over the build area platform 12 toform a layer 58 of build material 16 thereon. As shown in FIG. 2A, onelayer 58 of the build material 16 has been applied.

The layer 58 has a substantially uniform thickness across the build areaplatform 12. In an example, the thickness of the layer ranges from about50 μm to about 300 μm, although thinner or thicker layers may also beused. For example, the thickness of the layer 58 may range from about 20μm to about 500 μm, or from about 30 μm to about 300 μm.

The build material 16 may be a polymeric build material, a ceramic buildmaterial, a metallic build material, or a composite build material.

The polymeric build material may be crystalline or semi-crystallinepolymers in powder form. Examples of crystalline or semi-crystallinepolymers include semi-crystalline thermoplastic materials with a wideprocessing window of greater than 5° C. (i.e., the temperature rangebetween the melting point and the re-crystallization temperature). Somespecific examples of the semi-crystalline thermoplastic materialsinclude polyamides (PAs) (e.g., PA 11/nylon 11, PA 12/nylon 12, PA6/nylon 6, PA 8/nylon 8, PA 9/nylon 9, PA 66/nylon 66, PA 612/nylon 612,PA 812/nylon 812, PA 912/nylon 912, etc.). Other examples of crystallineor semi-crystalline polymers suitable for use as the build material 16include polyethylene, polypropylene, and polyoxomethylene (i.e.,polyacetals). Still other examples of suitable polymeric build materials16 include polystyrene, polycarbonate, polyester, polyurethanes, otherengineering plastics, and blends of any two or more of the polymerslisted herein. Core shell polymer particles of these materials may alsobe used.

Other examples of the build material 16 include ceramic particles.Examples of suitable ceramic particles include oxides, carbides, andnitrides. Some specific examples include alumina (Al₂O₃), glass, siliconmononitride (SiN), silicon dioxide (SiO₂), zirconia (ZrO₂), titaniumdioxide (TiO₂), or combinations thereof. As an example, 30 wt % glassmay be mixed with 70 wt % alumina.

Examples of the metal build material include copper (Cu), zinc (Zn),niobium (Nb), tantalum (Ta), silver (Ag), gold (Au), platinum (Pt),palladium (Pd), indium (In), bismuth (Bi), tin (Sn), lead (Pb), gallium(Ga), and alloys thereof. While more costly, osmium (Os), rhodium (Rh),ruthenium (Ru), and iridium (Ir) may also be used.

Composite build materials may include mixtures of polymer particles andinorganic particles. As examples, any of the previously listed polymerparticles may be combined with any of the previously listed ceramicparticles to form the composite build material.

The build material 16 may have a melting or softening point ranging fromabout 50° C. to about 4000° C. As examples, ceramic particles having amelting point ranging from about 600° C. to about 4000° C. may be used,metal particles having a melting point ranging from about 200° C. toabout 3500° C. may be used, or polymers having a melting or softeningpoint ranging from about 75° C. to about 400° C. may be used.

The build material 16 may be made up of similarly sized particles ordifferently sized particles. The term “size” or “particle size” is usedherein to describe at least the build material 16. The size or particlesize generally refers to the diameter or average diameter, which mayvary, depending upon the morphology of the individual particle. In anexample, the respective particle may have a morphology that issubstantially spherical. A substantially spherical particle (i.e.,spherical or near-spherical) has a sphericity of >0.84. Thus, anyindividual particles having a sphericity of <0.84 are considerednon-spherical (irregularly shaped). The particle size of thesubstantially spherical particle may be provided by its largestdiameter, and the particle size of a non-spherical particle may beprovided by its average diameter (i.e., the average of multipledimensions across the particle) or by an effective diameter, which isthe diameter of a sphere with the same mass and density as thenon-spherical particle.

In an example, the average size of the particles of the build material16 ranges from about 0.01 μm to about 500 μm. As an example, thepolymeric and/or metal build material may have a particle size rangingfrom about 5 μm to less than 200 μm. As another example, the ceramicbuild material may have a particle size ranging from about 0.05 μm toabout 100 μm.

It is to be understood that build material 16 may include, in additionto the polymer, ceramic, metal or composite particles, a charging agent,a flow aid, or combinations thereof. Charging agent(s) may be added tosuppress tribo-charging. Flow aid(s) may be added to improve the coatingflowability of the build material 16. In an example, each of thecharging agent and/or the flow aid may be added in an amount rangingfrom greater than 0 wt % to less than 5 wt % based upon the total wt %of the build material 16 used.

After the build material 16 is applied, the electronic agent 30 and thefusing agent 32 are selectively applied, and the build material layer 58(with and/or without agents 30, 32 thereon) is exposed toelectromagnetic radiation. FIGS. 2A through 2C specifically depict thefinal printing pass and heating event of the method. The details of thisexample of the method will be described further below.

The electronic agent 30 may be used to impart any electronic property toregion(s) of the layer and/or part that is formed. The electronicproperty may be electrical conductivity, semi-conductivity, and/or anelectrically insulating property. As examples, the region(s) exhibitingthe electronic property may form anti-static surface coatings (e.g.,scratch-tolerant surface conductivity for static-related applications),capacitors, resistors, inductors, conductive traces, vias, and morecomplex geometry electronic components.

The electronic agent 30 may be an aqueous formulation that includes aconductive material, a semi-conductive material, and/or an insulatingmaterial. The electronic agent 30 may include one of the materials, or acombination of the materials in order to enhance the compatibility witha particular build material and/or to enhance the electronic property.For examples, the electronic agent 30 may include a combination ofconductive materials to enhance the conductive electronic property, ormay include a combination of a semi-conductive material and aninsulating material to modify the electronic property. Some specificexamples of material combinations include: a combination of carbonnanotubes, silver nanoparticles and a PEDOT:PSS polymer to enhanceconductive properties; a combination of quantum dots and semi-conductingpolymers to enhance semi-conducting properties; a combination ofinsulating polymer and insulating nanoparticles to enhance insulatingproperties; and a combination of silver nanoparticles and carbon blackto create an electronic feature with a specific conductivity, forinstance, a resistor of specific resistance.

In an example, the electronic agent 30 may be an aqueous formulationthat includes a conductive material 31. Examples of the conductivematerial 31 include transition metal (e.g., silver, copper, gold,platinum, palladium, chromium, nickel, zinc, tungsten, etc.)nanomaterials (e.g., nanoparticles, nanorods, nanowires, nanotubes,nanosheets, etc.). The conductive material 31 may also include metalalloy nanomaterials, such as Au—Ag, Ag—Cu, Ag—Ni, Au—Cu, Au—Ni,Au—Ag—Cu, or Au—Ag—Pd.

Examples of other conductive materials 31 include conductive oxides(e.g., indium tin oxide, antimony oxide, zinc oxide, etc.), conductingpolymers (e.g., poly(3,4-ethylenedioxythiophene) polystyrene sulfonate(PEDOT:PSS), polyacetylene, polythiophenes, any other conjugatedpolymer, etc.), carbonaceous nanomaterials (e.g., graphene (single ormulti-layer), carbon-nanotubes (CNTs, single or multi-walled), graphenenanoribbons, fullerenes, etc.), and reactive metal systems.

Examples of reactive metal systems for use in the electronic agent 30can include a transition metal in the form of a metal organicdecomposition salt or metal oxide. Under certain conditions, the metalorganic decomposition salt or metal oxide in the electronic agent 30 canform elemental conductive nanomaterials 31 in situ after being printedonto the build material 16. The elemental conductive nanomaterials 31formed can then be sintered together to form a conductive matrix 31′(see FIG. 2B). In some examples, a reducing agent can be reacted withthe metal salt or metal oxide to produce elemental conductivenanomaterials 31. In one example, a reducing agent can be underprintedonto the powder bed before the electronic agent 30. In another example,a reducing agent can be overprinted over the electronic agent 30. Ineither case, the reducing agent can be reacted with the metal salt ormetal oxide to form elemental conductive nanomaterials 31 before thebuild material 16 is cured. Suitable reducing agents can include, forexample, glucose, fructose, maltose, maltodextrin, trisodium citrate,ascorbic acid, sodium borohydride, ethylene glycol, 1,5-pentanediol,1,2-propylene glycol, hydrazine, formic acid, and others.

In some examples, the conductive material 31 may be other non-transitionmetal nanomaterials. The non-transition metal nanomaterials can includelead, tin, bismuth, indium, gallium, and others. In some examples,soldering alloys may be included. The soldering alloys can includealloys of lead, tin, bismuth, indium, zinc, gallium, silver, copper, invarious combinations. In certain examples, the soldering alloys can beprinted in locations that are to be used as soldering connections forprinted electrical components. The soldering alloys can be formulated tohave low melting temperatures useful for soldering, such as less than230° C. Examples of the semi-conductive material that may be used in theelectronic agent 30 include semi-conducting nanomaterials(nanoparticles, nanorods, nanowires, nanotubes, nanosheets, etc.),semi-conducting metal oxides (e.g., tin oxide, antimony oxide, indiumoxide, etc.), semi-conducting polymers (e.g., PEDOT:PSS, polythiophenes,poly(p-phenylene sulfide), polyanilines, poly(pyrrole)s,poly(acetylene)s, poly(p-phenylene vinylene), polyparaphenylene, and anyother conjugated polymer, etc.), and semi-conducting small molecules(i.e., having a molecular mass less than 5,000 Daltons, e.g., rubrene,pentacene, anthracene, aromatic hydrocarbons, etc.). Some specificexamples of the semi-conducting nanomaterials include quantum dots,III-V or II-VI semiconductors, Si, Ge, transition metal dichalcogenides(WS2, WSe2, MoSes, etc.), graphene nanoribbons, semiconducting carbonnanotubes, and fullerenes and fullerene derivatives.

The previously described fullerenes, conducting or semi-conducting metaloxides, and conducting or semi-conducting polymers may besemi-conductive, in that they have a finite conductivity. However, thisconductivity may often be sufficient for conductive applications. Thematerial may be considered conductive or semi-conductive depending uponthe geometry and/or in what combination with other electronic componentsit is utilized.

Examples of the insulating (dielectric) material that may be used in theelectronic agent 30 include insulating nanomaterials (nanoparticles,nanorods, nanowires, nanotubes, nanosheets, etc.), colloids, or sol-gelprecursors, such as hexagonal boron nitride, metal and semiconductingoxides, metal and semiconducting nitrides, metal oxide sol-gelprecursors (e.g., metal alkoxides, metal chlorides, etc.), siliconsol-gel precursors (silicates), or solid electrolytes. Other examples ofthe insulating material include insulating polymers (e.g., polylacticacid, fluoropolymers, polycarbonate, acrylics, polystyrene, SU-8, etc.)and insulating small molecules (i.e., having a molecular mass less than5,000 Daltons, e.g., benzocyclobutane, paraffins, organic dyes, etc.).

While the examples disclosed herein refer to the conductivematerial/nanomaterials 31, it is to be understood that any of the othermaterials, such as semi-conductive materials and/or insulating materialsmay be used instead of or in combination with the conductivenanomaterials 31. It is to be understood that the electronic material inthe electronic agent 30 will depend upon the type of electronic propertythat is to be imparted to the region(s).

The average particle size, diameter, or other dimension of theconductive materials 31, semi-conductive materials, and/or insulatingmaterials may range from about 1 nm to about 200 nm.

The conductive nanomaterials 31 (or semi-conductive materials, if used)may be stabilized by a dispersing agent at surfaces thereof. In oneexample, the dispersing agent is a weakly bound ligand that passivatesthe surface of the conductive nanomaterials 31. These weakly boundligands may be molecules that attach to the nanomaterial surface througha sulfonic acid, phosphonic acid, carboxylic acid, dithiocarboxylicacid, phosphonate, sulfonate, thiol, carboxylate, dithiocarboxylate,amine, or pyridine functional group. As an example, the weakly boundligand may contain an alkyl group having from 3-20 carbon atoms, withone of the above moieties at an end of the alkyl chain. Examples of suchmolecules include dodecanoic acid, triethylenetetramine or anotheralkylamine, an alkylthiol, or 4-dimethylaminopyridine.

In further examples, the dispersing agent may be a polymeric dispersingagent, such as polyvinylpyrrolidone (PVP), polyvinylalcohol (PVA),polymethylvinylether, poly(acrylic acid) (PAA), nonionic surfactants,and polymeric chelating agents. These dispersing agents can bind to thesurfaces of the elemental transition metal nanomaterials throughchemical and/or physical attachment. Chemical bonding can include acovalent bond, hydrogen bond, coordination complex bond, ionic bond, orcombinations thereof. Physical attachment can include attachment throughvan der Waal's forces, dipole-dipole interactions, or a combinationthereof.

In an example, the electronic agent 30 can be a silver ink that includessilver nanoparticles dispersed by a dispersing agent. Examples ofcommercially available silver inks include Mitsubishi® NBSIJ-MU01available from Mitsubishi Paper Mills Limited, Methode® 9101 availablefrom Methode Electronics, Inc., Methode® 9102 available from MethodeElectronics, Inc., NovaCentrix™ JS-B40G available from NovaCentrix, andothers.

The concentration of conductive nanomaterials 31 (or other suitableconductive, semi-conductive, and/or insulating material) in theelectronic agent 30 may vary. However, higher conductive materialconcentrations may provide better conductivity due to a larger amount ofconductive material being deposited on the build material 16. When lowerconductive material concentrations are used, more electronic agent 30may be applied to achieve the desired amount of conductive material 31,and therefore the desired amount of conductivity, in the conductiveregion 52 of the 3D part 50. As an example, to achieve desirableconductivity, the electronic agent 30 may include at least 15 wt % ofsilver nanoparticles, and be applied in an amount sufficient to includeat least 20 wt % of silver nanoparticles in the conductive region 52. Inother examples, the electronic agent 30 can contain from about 5 wt % toabout 50 wt % of the conductive nanomaterials 31 (or other suitableconductive, semi-conductive, and/or insulating material), with respectto the entire weight of the electronic agent 30. In further examples,the electronic agent 30 can contain from about 10 wt % to about 30 wt %of the conductive nanomaterials 31 (or other suitable conductivematerial), with respect to the entire weight of the electronic agent 30.

In addition to the conductive material 31 (or other suitable conductive,semi-conductive, and/or insulating material), the aqueous formulation ofthe electronic agent 30 may also include water, a co-solvent, asurfactant, a pH adjuster, a biocide, and/or an anti-kogation agent.

Examples of suitable co-solvents include 2-pyrrolidinone,N-methylpyrrolidone, 1-(2-hydroxyethyl)-2-pyrrolidinone, 1,6-hexanediolor other diols (e.g., 1,5-Pentanediol, 2-methyl-1,3-propanediol, etc.),triethylene glycol, tetraethylene glycol, tripropylene glycol methylether, or the like, or combinations thereof. Whether used alone or incombination, the total amount of the co-solvent(s) ranges from about 1wt % to about 60 wt % of the total wt % of the electronic agent 30.

Examples of suitable surfactants include a self-emulsifiable, nonionicwetting agent based on acetylenic diol chemistry (e.g., SURFYNOL® SEFfrom Air Products and Chemicals, Inc.), a nonionic fluorosurfactant(e.g., CAPSTONE® fluorosurfactants from DuPont, previously known asZONYL FSO), and combinations thereof. In other examples, the surfactantis an ethoxylated low-foam wetting agent (e.g., SURFYNOL® 440 orSURFYNOL® CT-111 from Air Products and Chemical Inc.) or an ethoxylatedwetting agent and molecular defoamer (e.g., SURFYNOL® 420 from AirProducts and Chemical Inc.). Still other suitable surfactants includenon-ionic wetting agents and molecular defoamers (e.g., SURFYNOL® 104Efrom Air Products and Chemical Inc.) or water-soluble, non-ionicsurfactants (e.g., TERGITOL™ TMN-6 from The Dow Chemical Company). Insome examples, it may be desirable to utilize a surfactant having ahydrophilic-lipophilic balance (HLB) less than 10.

Whether a single surfactant is used or a combination of surfactants isused, the total amount of surfactant(s) in the electronic agent 30 mayrange from about 0.5 wt. % to about 1.5 wt. % based on the total wt. %of the electronic agent 30.

pH adjusters may be used to control the pH of the electronic agent 30.From 0 wt % to about 2 wt % (of the total wt % of the electronic agent30) of the pH adjuster, for example, can be used.

Examples of suitable biocides include an aqueous solution of1,2-benzisothiazolin-3-one (e.g., PROXEL® GXL from Arch Chemicals,Inc.), quaternary ammonium compounds (e.g., BARDAC® 2250 and 2280,BARQUAT® 50-65B, and CARBOQUAT® 250-T, all from Lonza Ltd. Corp.), andan aqueous solution of methylisothiazolone (e.g., KORDEK® MLX from TheDow Chemical Co.). The biocide or antimicrobial may be added in anyamount ranging from about 0.1 wt. % to about 5 wt. % with respect to thetotal wt. % of the electronic agent 30.

An anti-kogation agent may be included in the electronic agent 30.Kogation refers to the deposit of dried ink (e.g., electronic agent 30)on a heating element of a thermal inkjet printhead. Anti-kogationagent(s) is/are included to assist in preventing the buildup ofkogation. Examples of suitable anti-kogation agents includeoleth-3-phosphate (e.g., commercially available as CRODAFOS™ O3A orCRODAFOS™ N-3 acid from Croda), or a combination of oleth-3-phosphateand a low molecular weight (e.g., <5,000) polyacrylic acid polymer(e.g., commercially available as CARBOSPERSE™ K-7028 Polyacrylate fromLubrizol). Whether a single anti-kogation agent is used or a combinationof anti-kogation agents is used, the total amount of anti-kogationagent(s) in the electronic agent 30 may range from about 0.1 wt. % toabout 5 wt. % based on the total wt. % of the electronic agent 30.

Examples of the fusing agent 32 are water-based dispersions including aradiation absorbing binding agent (i.e., an active material). The amountof the active material in the fusing agent 32 may depend upon howabsorbing the active material. In an example, the fusing agent 32 mayinclude the active material and be applied in an amount sufficient toinclude at least 0.01 wt % of the active material in the 3D part 50.When the active material is black, even this low amount can produce ablack colored part. Higher weight percentages may darken the color.

The active material may be any infrared light absorbing colorant. In anexample, the active material is a near infrared light absorber. Any nearinfrared colorants, e.g., those produced by Fabricolor, Eastman Kodak,or Yamamoto, may be used in the fusing agent 32. As one example, thefusing agent 32 may be an ink formulation including carbon black as theactive material. Examples of this ink formulation are commercially knownas CM997A, 516458, C18928, C93848, C93808, or the like, all of which areavailable from Hewlett-Packard Company. As another example, the fusingagent 32 may be an ink formulation including near infrared absorbingdyes as the active material. Examples of this ink formulation aredescribed in U.S. Pat. No. 9,133,344, incorporated herein by referencein its entirety. Some examples of the near infrared absorbing dye arewater soluble near infrared absorbing dyes selected from the groupconsisting of:

and mixtures thereof. In the above formulations, M can be a divalentmetal atom (e.g., copper, etc.) or can have OSO₃Na axial groups fillingany unfilled valencies if the metal is more than divalent (e.g., indium,etc.), R can be any C1-C8 alkyl group (including substituted alkyl andunsubstituted alkyl), and Z can be a counterion such that the overallcharge of the near infrared absorbing dye is neutral. For example, thecounterion can be sodium, lithium, potassium, NH₄ ⁺, etc.

Some other examples of the near infrared absorbing dye are hydrophobicnear infrared absorbing dyes selected from the group consisting of:

and mixtures thereof. For the hydrophobic near infrared absorbing dyes,M can be a divalent metal atom (e.g., copper, etc.) or can include ametal that has Cl, Br, or OR′ (R′═H, CH₃, COCH₃, COCH₂COOCH₃,COCH₂COCH₃) axial groups filling any unfilled valencies if the metal ismore than divalent, and R can be any C1-C8 alkyl group (includingsubstituted alkyl and unsubstituted alkyl).

The fusing agent 32 is an aqueous formulation that may also include anyof the previously listed co-solvent(s), surfactant(s), pH adjuster(s),biocide(s), and/or anti-kogation agent(s) in the previously describedamounts (except that the wt % is based on the total wt % of the fusingagent 32). The aqueous nature of the fusing agent 32 enables the fusingagent 32 to penetrate, at least partially, into the layer 58 of thebuild material 16. The presence of a co-solvent and/or a surfactant inthe fusing agent 32 may assist in obtaining a particular wettingbehavior.

As mentioned above, the example method shown in FIGS. 2A through 2Cinvolves the selective application of the electronic agent 30 and thefusing agent 32 and the exposure of the build material 16 toelectromagnetic radiation to ultimately form a fused layer 56. It isgenerally desirable for the fused layer 56 to be mechanically strong andfor the conductive region 52 to exhibit a sufficient electronic propertyfor the application in which the 3D part 50 will be used. Exposure tohigh heat can create a mechanically strong part, but can alsodeleteriously affect electronic properties, such as conductivity. Inthis example of the method, the electronic agent 30 is applied in aplurality of passes, the fusing agent 32 is applied in a single pass,and several heating events are performed throughout the passes, and theorder of the passes and events are controlled in order to control themechanical property and the electronic property of the fused layer 56that is formed.

In an example, to control the conductive or semi-conductive property,the electronic agent 30 may be applied at a maximum loading in severalprinting passes (2 or more) and the fusing agent 32 may be appliedduring the final printing pass alone (so that radiation absorption doesnot occur during each heating event when a highly absorbing activematerial is utilized). In other examples to control the conductive orsemi-conductive property, an applicator 28A may be selected thatdispenses high enough drop weights of the electronic agent 30 to achievethe desired conductivity without utilizing maximum loadings.

To control the mechanical property, a suitable number of heating eventsare utilized, but the heating events are spread out throughout theprinting passes to avoid over-heating and to manage thermaldistribution.

As an example of this method, one or two heating events may be performedprior to the selective application of either the electronic agent 30 orthe fusing agent 32. The heating event(s) may be performed to preheatthe build material 16, and thus the heating temperature may be below themelting point or softening point of the build material 16. As such, thetemperature selected will depend upon the build material 16 that isused. As examples, the heating temperature may be from about 5° C. toabout 50° C. below the melting point or softening point of the buildmaterial 16. The preheating event(s) may be accomplished using anysuitable heat source (e.g., radiation source 46, 46′) that exposes allof the build material 16 to the heat. As an example of two preheatingevents, both of the moving lamps 46 may be turned on and passed over thebuild material 16 one time.

After preheating, a first printing pass may be performed, during whichthe electronic agent 30 is selectively applied on portion(s) of thebuild material 16 that are to become conductive region(s) 52 in thefused layer 56. In other examples, the electronic agent 30 isselectively applied on portion(s) of the build material 16 that are tobecome semi-conductive region(s) or insulating region(s), depending uponthe type of electronic material that is contained within the electronicagent 30. The electronic agent 30 may be dispensed using the applicator28A, and may be dispensed at a maximum loading (e.g., 255 contone (whichrefers to the number of drops, which is divided by 256, that will beplaced on average onto each pixel)). The maximum loading may varydepending on the print resolution, drop weight of the applicator 28A,28B, 28C, 28D, the concentration of the agent, the number of passes, theeffective printing slots of the applicator 28A, 28B, 28C, 28D, and thethickness of the build material layer 58. As an example, for a 1200×1200dpi (drops per inch), 140 mg/cc of solid silver may be dispensed using a15% solids electronic agent 30 with three passes from one slot at a dropweight of 14 ng onto a 100 nm thick layer 58.

The first printing pass may be associated with one heating event. Forexample, immediately before, during, or immediately after the electronicagent 30 is dispensed, the build material 16 may be exposed to a heatingevent using radiation source 46, 46′. For this heating event, one of themoving lamps 46 may be turned on, or the overhead lamp 46′ may be used.It may be desirable for the heating event to take place immediatelyfollowing the application of the electronic agent 30, and thus the lamp46 that is turned on may depend upon its position with respect to theapplicator 28A and well as the printing direction.

One or more additional printing passes, during which the electronicagent 30 is selectively dispensed, may then be performed, and each ofthese additional printing passes may be associated with a heating event(e.g., the passes may be immediately preceded by one heating event, orimmediately followed by one heating event, or preceded and followed byrespective heating events). When one heating event is performed, one ofthe moving lamps 46 or the overhead lamp 46′ may be used, and when twoheating events are performed, both of the moving lamps 46 may be turnedon or the overhead lamp 46′ may be turned on for a longer period oftime.

The plurality of printing passes are used to increase the amount ofelectronic agent 30 (and thus, in this example, the amount of theconductive nanomaterials 31) that is applied to a single layer of buildmaterial 16. The plurality of heating events are used to counteract acooling effect that may be brought on by the large amount of electronicagent 30 that is applied, to evaporate liquid from the appliedelectronic agent 30, to heat the build material 16 without fusing/curingthe build material 16 (because the fusing agent 32 has not yet beendispensed), and/or to begin to sinter the nanomaterials 31 to form aconductive matrix 31′. The timing of any of the heating event(s) maydepend, in part, on the melting or softening point of the build material16, the type and amount of any agent(s) 30, 32, 34, 36 that are appliedto the build material, etc.

As the conductive materials 31 are reduced in size, the temperature atwhich the materials 31 are capable of being sintered can also bereduced. Therefore, using elemental transition metal nanomaterials orother conductive nanomaterials 31 in the electronic ink 30 can allow thenanomaterials 31 to sinter and form a conductive matrix 31′ of sinterednanomaterials at relatively low temperatures. For example, theconductive materials 31 in the electronic agent 30 can be capable ofbeing sintered at or below the temperature reached during fusing/curing(i.e., the final heating event). The particular temperatures used in theheating events throughout the process can vary depending on the melt,softening, or fusing temperature of the particular build material 16used. In an example, the conductive nanomaterials 31 can be capable ofbeing sintered at a temperature ranging from 20° C. to 400° C., whichmay be achieved during the heating event(s) immediately following theapplication of the electronic agent 30 without the fusing agent 32. Asused herein, the temperature at which the conductive materials 31 arecapable of being sintered refers to the lowest temperature at which thematerials 31 will become sintered together, forming a conductive matrix31′ of sintered materials. It is to be understood that temperaturesabove this lowest temperature will also cause the materials 31 to becomesintered.

It is to be understood that after any of printing pass/heating eventcombinations, and prior to the next printing pass, the build material 16may be allowed to cool to a threshold temperature. In one example, thecooling may be passive cooling. The mechanism for passive cooling may bethermal radiation escaping from the heated portion(s) of the layer 58,convection to the surrounding environment, and/or conduction into coolerportions of the layer 58. When the layer 58 is not the first layer(i.e., the bottom most layer of the part 50 being formed), the mechanismfor passive cooling may additionally include conduction into cooler,previously fused layers below the layer 58. Passive cooling involves thesystem 10 waiting to perform the next printing pass until thetemperature of the build material 16 reaches the threshold temperature.The threshold temperature generally ranges from about 10° C. below toabout 100° C. below the melting or softening point of the build material16 that is being used. The system 10 may include a temperature sensor,thermal imaging camera, thermocouple, etc. to determine when thethreshold temperature is reached. The timing for passive cooling may bedifferent following different heating events, depending, in part uponthe temperature of the build material 16 (which can depend upon theamount of electronic agent 30 applied in any given pass).

During a final printing pass of this example method, both the electronicagent 30 and the fusing agent 32 are dispensed on at least a portion ofthe build material layer 58. This is depicted in FIG. 2A. In thisexample, the electronic agent 30 and the fusing agent 32 are dispensedonto the same portion(s), which have already been exposed to electronicagent 30 and heating events. The portion(s) will form a conductiveregion 52 (or semi-conductive or insulating depending upon theelectronic agent 30 that is used) of the fused layer 56. Both theelectronic agent 30 and the fusing agent 32 are capable of penetratinginto the spaces between the build material particles 16, as shown inFIG. 2B. Moreover, it is to be understood that some of the conductivenanomaterials 31 from the previously dispensed electronic agent 30 mayalready be sintered when the final printing pass takes place, and thatthe freshly applied electronic agent 30 and the fusing agent 32 arecapable of penetrating into the spaces between the build materialparticles 16 and the conductive transition metal matrix 31′ that hasformed.

Immediately preceding, during, or immediately following the finalapplication of the electronic agent 30 and the application of the fusingagent 32, the build material 16 can be exposed to a final heating event,as shown in FIG. 2C. During this heating event, the fusing agent 32facilitates fusing of the build material particles 16 in contacttherewith by absorbing energy from the electromagnetic radiation andconverting the energy to heat. This raises the temperature of the buildmaterial 16 (in contact with the fusing agent 32) above the melting orsoftening point of the build material 16. As such, the build material 16fuses together to form a matrix of fused build material 17. When theelectronic agent 30 and the fusing agent 32 are applied in the sameportion(s), the electronic agent 30 may have a cooling effect due to therelatively large amount of electronic agent 30 that may be dispensed toachieve the desired electrical property. As such, the amount of fusingagent 32 applied should account for this cooling effect so that theportion(s) are heated to or above the melting or softening point of thebuild material 16. Similarly, when the electronic/fusing agent 30′includes the radiation absorber (discussed further in reference to FIGS.4A-4D), the amount of the radiation absorber included in theelectronic/fusing agent 30′ should account for the cooling effect of theelectronic/fusing agent 30′ so that the portion(s) are heated to orabove the melting or softening point of the build material 16.

Additionally during the final heating event, the conductivenanomaterials 31 in the electronic ink 30 can form additional conductivematrices 31′ that becomes interlocked with the fused build material 17.

In the example shown in FIG. 2C, the entire fused layer 56 isconductive.

It is to be understood that the various passes and heating eventsdescribed in reference to FIGS. 2A through 2C are performed on a singlelayer 58 of the build material 16 (i.e., prior to the application ofadditional build material 16). After the fused layer 56 is formed, a newlayer of build material 16 may be applied to the fused layer 56 and thevarious passes and heating events may be repeated to form another fusedlayer on the fused layer 56. These processes may be repeated as manytimes is desirable to form the final 3D part 50.

Another example of the method is shown in FIGS. 3A through 3D. Thisexample is similar to the example described in reference to FIGS. 2Athrough 2C, except that the fusing agent 32 is applied to form both aconductive region 52 and an insulating region 54, and the detailingagent 34 is applied for thermal management.

As shown in FIG. 3A, this example method involves applying the buildmaterial 16. The build material 16 may be applied to form a layer 58 aspreviously described.

After the build material 16 is applied, the electronic agent 30 isselectively applied to a portion 60 of the build material layer 58 in aplurality of passes, the fusing agent 32 is selectively applied to theportion 60 and to another portion 62 in a single pass, the detailingagent 34 is applied to at least the portion 62 in a single pass or aplurality of passes, and several heating events are performed throughoutthe passes. The order of the passes and heating events is controlled inorder to control the mechanical property and the conductive property ofthe fused layer 56′ that is formed. It is to be understood that FIGS. 3Athrough 3D specifically depict the final printing pass and heating eventof the method to form the fused layer 56′.

In an example, to control the conductive or semi-conductive property,the electronic agent 30 is applied at a maximum loading in severalprinting passes (2 or more) and the fusing agent 32 is applied duringthe final printing pass alone (so that radiation absorption does notoccur during each heating event when a highly absorbing active materialis utilized). In other examples to control the conductive orsemi-conductive property, an applicator 28A may be selected thatdispenses high enough drop weights of the electronic agent 30 to achievethe desired conductivity without utilizing maximum loadings.

To control the mechanical property, a suitable number of heating eventsare utilized, but the heating events are spread out throughout theprinting passes to avoid over-heating and to manage thermaldistribution. Also to control the mechanical property, the detailingagent 34 is utilized for thermal management (i.e., controls a maximumtemperature that the build material 16 in contact therewith can reach).

As an example of this method, one or two heating events may be performedprior to the selective application of any of the agents 30, 32, 34. Thisheating event may be performed to preheat the build material 16 in themanner previously described.

After preheating, a first printing pass may be performed, during whichthe electronic agent 30 is selectively applied on portion(s) 60 of thebuild material 16 that are to become conductive region(s) 52 in thefused layer 56′. The electronic agent 30 may be dispensed using theapplicator 28A, and may be dispensed at a maximum loading (e.g., 255contone). The first printing pass may involve the application of theelectronic agent 30 alone, or the application of the electronic agent 30in portion 60 and the detailing agent 34 in portion(s) 62 or 62 and 64.

The detailing agent 34 may be selectively applied using any suitableapplicator, such as applicator 28C.

The detailing agent 34 may be water alone. The detailing agent 34 mayalso include a surfactant, a co-solvent, and a balance of water. In someexamples, the detailing agent 34 consists of these components, and noother components. In some instances, the detailing agent 36 furtherincludes an anti-kogation agent, a biocide, or combinations thereof. Thecomponents of the detailing agent 34 may be similar to the surfactants,co-solvents, anti-kogation agents, and biocide described above inreference to the electronic agent 30 and/or fusing agent 32. Thedetailing agent 34 may also include a colorant, but it is to beunderstood that this colorant may absorb the radiation used for heatingand fusing, but to a lesser extent than the colorant in the fusing agent32. Overall, the heating effect of the colorant in the detailing agent34 is much less than the cooling effect produced by other components ofthe detailing agent 34. The colorant may be desirable when the detailingagent 34 is applied to the portion 62 (which ultimately also has thefusing agent 32 applied thereto as well).

When used in the first printing pass, the detailing agent 34 may beapplied to actively cool portion(s) 62, 64 of the build material 16 thatdo not have the electronic agent 30 applied thereto. The detailing agent34 may also be applied to actively cool portion(s) 60 that have theelectronic agent 30 applied thereto. The detailing agent 34 may providean evaporative cooling effect that reduces the temperature of the buildmaterial 16 in contact with the detailing agent 34 during the heatingevent(s) associated with the first printing pass. In the first printingpass, the amount of the detailing agent 34 applied in the portion 62 andthe portion 64 may be the same. The use of the detailing agent 34 inthis manner may eliminate the need for passive cooling, because thebuild material 16 exposed to the detailing agent 34 is maintained at orbelow the threshold temperature during the subsequent heating event(s).Alternatively, passive cooling may also be used in order to ensure thatthe build material 16 exposed to the detailing agent 34 is at or belowthe threshold temperature before the method proceeds with anotherprinting pass. The time period for passive cooling after the first passand heating event(s) may be shorter when the detailing agent 34 isutilized (compared to when it is not utilized).

The first printing pass may be associated with one heating event. Forexample, immediately before, during, or immediately after the electronicagent 30 is dispensed or the electronic agent 30 and the detailing agent34 are dispensed, the build material 16, which may have the agent(s) 30or 30, 34 thereon, may be exposed to a heating event using radiationsource 46, 46′.

One or more additional printing passes, during which the electronicagent 30 is selectively dispensed or the electronic agent 30 and thedetailing agent 34 are selectively dispensed, may then be performed, andeach of these additional printing passes may be combined with one or twoheating events.

The plurality of printing passes are used to increase the amount ofelectronic agent 30 (and thus in some instances the amount of theconductive nanomaterials 31) that is applied to a single layer of buildmaterial 16, and in some instances, to apply the detailing agent 34 forthermal management of the portion(s) 60, 62, 64 of the build material16. The plurality of heating events are used to counteract a coolingeffect that may be brought on by the large amount of electronic agent 30that is applied, to evaporate liquid from the applied electronic agent30, to heat the build material 16 or maintain the temperature of thebuild material 16 without fusing/curing the build material 16 (becausethe fusing agent 32 has not yet been dispensed), and/or to begin tosinter the nanomaterials 31 to form a conductive matrix 31′.

If the detailing agent 34 is not used in the subsequent pass(es) or thebuild material 16 temperature is above the threshold temperature afterthe heating event(s), it is to be understood that the build material 16may be allowed to passively cool to or below the threshold temperatureprior to the next printing pass. The timing for passive cooling may bedifferent following different heating passes, depending, in part uponthe temperature of the build material 16, which can depend upon theamount of electronic agent 30 and/or detailing agent 34 applied in anygiven pass. Moreover, in this example of the method, more than onethreshold temperature may be used to determine the timing of the nextpass. For example, different portions 60, 62, 64 may have differentthreshold temperatures.

During a final printing pass of this example method, the electronicagent 30 is dispensed into the portion 60 (as shown in FIG. 3A); thefusing agent 32 is dispensed on the portion 60 with the electronic agent30 and on another portion 62 (as shown in FIG. 3B); and the detailingagent 34 is dispensed on the portion 62 and, in some instances, on theportion 64 (as shown in FIG. 3C).

In this example, the electronic agent 30 and some of the fusing agent 32are dispensed onto the same portion 60, which has already been exposedto electronic agent 30 and heating events. The portion 60 will form aconductive region 52 of the fused layer 56′. Both the electronic agent30 and the fusing agent 32 are capable of penetrating into the spacesbetween the build material particles 16 in portion 60, as shown in FIG.3B. Moreover, it is to be understood that some of the conductivenanomaterials 31 from the previously dispensed electronic agent 30 mayalready be sintered when the final printing pass takes place, and thatthe freshly applied electronic agent 30 and the fusing agent 32 arecapable of penetrating into the spaces between the build materialparticles 16 and the conductive matrix 31′ that has formed (see FIG.3B).

In this example, some of the fusing agent 32 is also dispensed onto theportion 62, which is not exposed to any electronic agent 30 and may havebeen exposed to detailing agent 34 in prior passes. The portion 62 willform a non-conductive or insulating region 54 of the fused layer 56′.The fusing agent 32 is capable of penetrating into the spaces betweenthe build material particles 16 in portion 62, as shown in FIG. 3B. Itis to be understood that an electronic agent 30 including an insulatingmaterial could also be applied to the portion 62 to form the insulatingregion 54.

In this example, some of the fusing agent 32 and the detailing agent 34are dispensed onto the same portion 62. As noted above, the portion 62will form a non-conductive or insulating region 54 of the fused layer56′. The amount of fusing agent 32 that is dispensed is enough to absorba desirable amount of radiation from the subsequently appliedelectromagnetic radiation, and the amount of detailing agent 34 that isdispensed is enough to keep the build material 16 in the portion 62 fromover-heating without preventing fusing. When used in portion 62, it maybe desirable for the detailing agent 34 to contain a colorant thatmatches the color of the fusing agent 32, but does not absorb theapplied electromagnetic radiation or does not absorb enough of theapplied electromagnetic radiation to initiate fusing.

Both the fusing agent 32 and the detailing agent 34 are capable ofpenetrating into the spaces between the build material particles 16 inportion 62, as shown in FIG. 3C.

Also as shown in FIG. 3C, the detailing agent 34 may be dispensed ontothe portion 64. Portion 64 does not have any fusing agent 32 appliedthereto, and thus will not fuse during the final heating event(s) andwill not be part of the final fused layer 56′. As an example, theportion(s) 64 may be outside of an edge boundary (i.e., the outermostportions where the fusing agent 32 is selectively deposited onto thebuild material 16 during 3D printing) of the fused layer 56′. Theselective application of the detailing agent 34 in these portion(s) 64can prevent the build material 16 in these area(s) from fusing and canalso prevent thermal bleed (i.e., heat transferring from the portion 62which is fused).

The amount of detailing agent applied in portion 62 and in portion 64depends on the thermal situation in each portion 62, 64. In theseportions 62, 64, the thermal situation may vary depending on the buildmaterial 16, the fusing agent 32, and/or the heating event conditions.

Before, during, or after the final pass in which the electronic agent30, the fusing agent 32, and the detailing agent 34 are dispensed, allof the build material 16 can be exposed to a final heating event, asshown in FIG. 3D. During this heating event, the fusing agent 32facilitates fusing of the build material particles 16 in contacttherewith (i.e., in portions 60 and 62) by absorbing energy from theelectromagnetic radiation and converting the energy to heat. This raisesthe temperature of the build material 16 (in contact with the fusingagent 32) above the melting or softening point of the build material 16.As such, the build material 16 fuses together to form a matrix of fusedbuild material 17. The fused build material 17 at the portion 62 formsthe insulating region 54 of the fused layer 56′. At portion 60, theconductive nanomaterials 31 in the electronic ink 30 can form additionalconductive matrices 31′ that becomes interlocked with the fused buildmaterial 17. The combination of the fused build material 17 and theconductive matrices 31′ forms the conductive region 52 of the fusedlayer 56′.

In the example shown in FIG. 3D, some of the build material 16 (atportion 64) remains unfused. This build material 16 may be removed fromthe fused layer 56′, and in some instances may be washed and reused inanother 3D printing process.

It is to be understood that the various passes and heating eventsdescribed in reference to FIGS. 3A through 3D are performed on a singlelayer 58 of the build material 16 (i.e., prior to the application ofadditional build material 16). After the fused layer 56′ is formed, anew layer of build material 16 may be applied to the fused layer 56′ andthe various passes and heating events may be repeated to form anotherfused layer on the fused layer 56′. These processes may be repeated asmany times is desirable to form the final 3D part 50.

In the example shown in FIGS. 3A through 3D, the conductive region 52could be fused prior to the last printing pass and heating event(s).This may be accomplished by dispensing the fusing agent 32 on theportion 60 during an earlier printing pass. In these instances, thedetailing agent 34 may be used in the portion 60 during subsequentprinting passes in order to keep the portion 60 from over fusing (e.g.,when the fusing agent 32 is highly absorbing and subsequent heatingevents are performed). Also in these instances, subsequent printingpasses may be performed without heating events until the final printingpass when it is desirable to fuse other portions, such as portion 62.

Still another example of the method is shown in FIGS. 3E, 3A, 3F and 3G.This example is similar to the example described in reference to FIGS.3A through 3D, except that the activating agent 36 is applied prior toany application of the electronic agent 30. While this example utilizesthe activating agent 36, it is to be understood that the use of theactivating agent 36 depends, in part, upon the electronic agent 30 thatis used. Activating agent 36 may not be utilized when the material 31does not have a passivated surface, when localized heating is used incombination with a higher melting point build material 16, or when theelectronic agent 30 does not require a physical or chemicaltransformation to achieve the desired electronic properties (e.g., whenthe electronic agent 30 includes PEDOT:PSS as the conductive material31).

In this example, the activating agent 36 is selectively applied to theportion 60 of the build material layer 58 in a plurality of passes andbefore the electronic agent 30, the electronic agent 30 is selectivelyapplied to the portion 60 in a plurality of passes, the fusing agent 32is selectively applied to the portion 60 and to another portion 62 in asingle pass, the detailing agent 34 is applied to at least the portion62 in a single pass or a plurality of passes, and several heating eventsare performed throughout the passes. The order of the passes and heatingevents is controlled in order to control the mechanical property and theconductive property of the fused layer 56″ that is formed. It is to beunderstood that FIGS. 3E and 3A together depict an example of the firstprinting pass, FIGS. 3E, 3A and 3F together depict an example of thefinal printing pass, and FIG. 3G depicts an example of the final heatingevent to form the fused layer 56″.

To control the conductive or semi-conductive property, the activatingagent 36 and the electronic agent 30 are applied at a maximum loading inseveral printing passes (2 or more), and the fusing agent 32 is appliedduring the final printing pass alone (so that radiation absorption doesnot occur during each heating event when the active material is highlyabsorbing). In other examples to control the conductive orsemi-conductive property, an applicator 28A may be selected thatdispenses high enough drop weights of the electronic agent 30 to achievethe desired conductivity without utilizing maximum loadings. To controlthe mechanical property, a suitable number of heating events areutilized, but the heating events are spread out throughout the printingpasses to avoid over-heating and to manage thermal distribution. Also tocontrol the mechanical property, the detailing agent 34 is utilized forthermal management.

As shown in FIG. 3E, this example method involves applying the buildmaterial 16. The build material 16 may be applied to form a layer 58 aspreviously described.

As an example of this method, one or two heating events may be performedprior to the selective application of any of the agents 30, 32, 34, 36.This heating event(s) may be performed to preheat the build material 16in the manner previously described.

After preheating, a first printing pass may be performed, during whichat least the activating agent 36 is selectively applied on portion(s) 60of the build material 16 that are to become conductive region(s) 52 inthe fused layer 56″. The first printing pass may involve the applicationof the activating agent 36 alone, the application of both the activatingagent 36 and the electronic agent 30, or the application of theactivating agent 36 and the electronic agent 30 in portion 60 and thedetailing agent 34 in portion(s) 62 or 62 and 64, or 60, 62 and 64.

After the build material 16 is applied, the activating agent 36 isselectively applied to the portion 60 where the electronic agent 30 willbe applied, as shown in FIG. 3E. The activating agent 36 may beselectively applied using any suitable applicator, such as applicator28D.

The activating agent 36 is a pretreat composition that may be used whenthe electronic ink 30 includes the dispersing agent at the surfaces ofthe conductive nanomaterials 31 (or other conductive, semi-conductive,and/or insulating material). The activating agent 36 includes a metalsalt that can react with dispersing agent to remove the dispersing agentfrom the nanomaterials 31. The removal of the dispersing agent canincrease the sintering between the conductive nanomaterials 31 andimprove the conductivity of the matrix 31′ formed of the sinterednanomaterials. As such, the metal salt may be said to activate thenanomaterials 31.

Examples of the metal salt that may be used in the activating agent 36include chloride salts, bromide salts, and iodide salts. The chloride,bromide, or iodide salts may be an alkali metal salt or an alkalineearth metal salt. Some specific examples include potassium chloride,sodium chloride, lithium chloride, calcium chloride, hydrochloride salt,magnesium chloride, manganese chloride, zinc chloride, nickel chloride,cobalt chloride, iron chloride, potassium bromide, sodium bromide,lithium bromide, potassium iodide, sodium iodide, lithium iodide, andcombinations thereof.

The activating agent 36 may be an aqueous solution that includes atleast the metal salt. In an example, the activating agent 36 may consistof water and the metal salt. In another example, the activating agent 36may include other components in addition to the water and the metalsalt. For example, the activating agent 36 may include any one or moreof the surfactants, co-solvents, anti-kogation agents, and biocidesdescribed above in reference to the electronic agent 30 and/or fusingagent 32.

The metal salt can be present in the activating agent 36 at aconcentration that is effective to remove the dispersing agent from thenanomaterials 31 in the electronic ink and to aid in forming conductiveregion(s) 52 using the electronic agent 30. In one example, theconcentration of metal salt in the activating agent 36 may range fromabout 0.1 wt % to about 15 wt % (based on the total wt % of the agent36). In another example, the metal salt concentration may range fromabout 0.5 wt % to about 10 wt %. In yet another example, the metal saltconcentration may range from about 1 wt % to about 5 wt %.

While FIG. 3E illustrates the application of the activating agent 36during the 3D printing method, it is to be understood that theactivating agent 36 could be dispensed onto the build material 16 priorto being used in the 3D printing system 10. As such, the activatingagent 36 could be used to pretreat the build material 16.

After the activating agent 36 is applied to the portion 60 of the buildmaterial 16 (either during printing or to pretreat the build material16), a heating event may be performed. This heating event may be used todry the activating agent 36 before the electronic agent 30 is applied.This heating event may be active, in that the radiation source 46, 46′is passed over the build material platform 12 or turned on. When thebuild material platform 12 is preheated to an elevated temperature thatcan dry the liquid from the activating agent 36, the heating event maynot be performed prior to the application of the electronic agent 30.

The method then moves to FIG. 3A, which illustrates the selectiveapplication of the electronic agent 30 onto the portion 60. In thisexample, when the electronic agent 30 is applied on the portion 60, thenanomaterials 31 can come into contact with the previously applied metalsalt, which can remove the dispersing agent from the nanomaterials 31and render them more suitable for sintering.

When the activating agent 36 is alone applied in the first pass (whichis associated with a heating event), the second pass may involve theapplication of the electronic agent 30 in the portion 60, with orwithout the application of the detailing agent 34 to actively coolportion(s) 62, 64 of the build material 16 that do not have theelectronic agent 30 applied thereto. In this example, the second passmay be associated with one or two heating events.

When the activating agent 36 and electronic agent 30 are appliedtogether in the first pass, the detailing agent 34 may also be applied(during the first pass) to actively cool portion(s) 62, 64 of the buildmaterial 16 that do not have the electronic agent 30 applied thereto. Inthis example, the first pass may be associated with one or two heatingevents.

In these examples, the detailing agent 34 may also be used in theportion 60 to keep the portion having the electronic agent 30 thereonfrom overheating.

When used in the first or second printing pass, the detailing agent 34may provide an evaporative cooling effect that reduces the temperatureof the build material 16 in contact with the detailing agent 34 duringthe heating event(s) taking place in conjunction with the first printingpass or the second printing pass. The use of the detailing agent 34 mayeliminate the need for passive cooling, because the build material 16exposed to the detailing agent 34 is maintained at or below thethreshold temperature during the subsequent heating event(s).Alternatively, passive cooling may also be used in order to ensure thatthe build material 16 exposed to the detailing agent 34 is at or belowthe threshold temperature before the method proceeds with anotherprinting pass.

One or more additional printing passes, during which the activatingagent 36 and the electronic agent 30 are selectively dispensed or theactivating agent 36, electronic agent 30 and the detailing agent 34 areselectively dispensed, may then be performed, and each of theseadditional printing passes may be associated with one or two heatingevents. With any of these additional printing passes, a heating eventmay follow the application of the activating agent 36 in order to drythe agent 36.

The plurality of printing passes are used to increase the amount ofactivating agent 36 and electronic agent 30 (and thus the amount of theconductive nanomaterials 31) that is applied to a single layer of buildmaterial 16, and in some instances, to apply the detailing agent 34 forthermal management of the portion(s) 62, 64 of the build material 16.The plurality of heating events are used to evaporate liquid from theapplied activating agent 36, to counteract a cooling effect that may bebrought on by the large amount of electronic agent 30 that is applied,to evaporate liquid from the applied electronic agent 30, to heat thebuild material 16 or maintain the temperature of the build material 16without fusing/curing the build material 16 (because the fusing agent 32has not yet been dispensed), and/or to begin to sinter the nanomaterials31 to form a conductive matrix 31′.

If the detailing agent 34 is not used in the subsequent pass(es) or thebuild material 16 temperature is above the threshold temperature afterthe heating event(s), it is to be understood that the build material 16may be allowed to passively cool to or below the threshold temperatureprior to the next printing pass.

During a final printing pass of this example method, the activatingagent 36 and electronic agent 30 are dispensed into the portion 60 (asshown in FIGS. 3E and 3A); the fusing agent 32 is dispensed on theportion 60 with the activating agent 36 and the electronic agent 30 andon another portion 62 (as shown in FIG. 3F); and the detailing agent 34is dispensed on the portion 62 and, in some instances, on the portion 64(as shown in FIG. 3F).

In this example, the activating agent 36, the electronic agent 30 andsome of the fusing agent 32 are dispensed onto the same portion 60,which has already been exposed to activating agent 36, electronic agent30, and heating events. The portion 60 will form a conductive region 52of the fused layer 56″. The agents 36, 30, 32 are capable of penetratinginto the spaces between the build material particles 16 in portion 60,as shown in FIG. 3F. Moreover, it is to be understood that some of theconductive nanomaterials 31 from the previously dispensed electronicagent 30 may already be sintered when the final printing pass takesplace, and that the freshly applied activating agent 36, electronicagent 30 and fusing agent 32 are capable of penetrating into the spacesbetween the build material particles 16 and the conductive matrix 31′that has formed (see FIG. 3F).

In this example, some of the fusing agent 32 is also dispensed onto theportion 62, which is not exposed to any activating agent 36 andelectronic agent 30 and may have been exposed to detailing agent 34 inprior passes. The portion 62 will form a non-conductive or insulatingregion 54 of the fused layer 56″. The fusing agent 32 is capable ofpenetrating into the spaces between the build material particles 16 inportion 62, as shown in FIG. 3F.

In this example, some of the fusing agent 32 and the detailing agent 34are dispensed onto the same portion 62. As noted above, the portion 62will form a non-conductive or insulating region 54 of the fused layer56″. The amount of fusing agent 32 that is dispensed is enough to absorba desirable amount of radiation from the subsequently appliedelectromagnetic radiation, and the amount of detailing agent 34 that isdispensed is enough to keep the build material 16 in the portion 62 fromover-heating without preventing fusing. When used in portion 62, it maybe desirable for the detailing agent 34 to contain a colorant thatmatches the color of the fusing agent 32, but does not absorb theapplied electromagnetic radiation or does not absorb enough of theapplied electromagnetic radiation to initiate fusing.

Both the fusing agent 32 and the detailing agent 34 are capable ofpenetrating into the spaces between the build material particles 16 inportion 62, as shown in FIG. 3F.

Also as shown in FIG. 3F, the detailing agent 34 may be dispensed ontothe portion 64. Portion 64 does not have any fusing agent 32 appliedthereto, and thus will not fuse during the final heating event(s) andwill not be part of the final fused layer 56′. As an example, theportion(s) 64 may be outside of an edge boundary of the fused layer 56″.The selective application of the detailing agent 34 in these portion(s)64 can prevent the build material 16 in these area(s) from fusing andcan also prevent thermal bleed (i.e., heat transferring from the portion62 which is fused).

Before, during, or after the final pass in which the activating agent36, the electronic agent 30, the fusing agent 32, and the detailingagent 34 are dispensed, all of the build material 16 can be exposed to afinal heating event, as shown in FIG. 3G. During this heating event, thefusing agent 32 facilitates fusing of the build material particles 16 incontact therewith (i.e., in portions 60 and 62) by absorbing energy fromthe electromagnetic radiation and converting the energy to heat. Thisraises the temperature of the build material 16 (in contact with thefusing agent 32) above the melting or softening point of the buildmaterial 16. As such, the build material 16 fuses together to form amatrix of fused build material 17. The fused build material 17 at theportion 62 forms the insulating region 54 of the fused layer 56″. Atportion 60, the conductive nanomaterials 31 in the electronic ink 30 canform additional conductive matrices 31′ that becomes interlocked withthe fused build material 17. The combination of the fused build material17 and the conductive matrices 31′ forms the conductive region 52 of thefused layer 56″.

In the example shown in FIG. 3G, some of the build material 16 (atportion 64) remains unfused. This build material 16 may be removed fromthe fused layer 56′, and in some instances may be washed and reused inanother 3D printing process.

It is to be understood that the various passes and heating eventsdescribed in reference to FIGS. 3E, 3A, 3F, and 3G are performed on asingle layer 58 of the build material 16 (i.e., prior to the applicationof additional build material 16). After the fused layer 56″ is formed, anew layer of build material 16 may be applied to the fused layer 56″ andthe various passes and heating events may be repeated to form anotherfused layer on the fused layer 56″. These processes may be repeated asmany times is desirable to form the final 3D part 50.

The examples shown in FIGS. 2 and 3 discuss dispensing the fusing agent32 in the final printing pass in order to avoid over-fusing. However,when the fusing agent 32 includes an active material that is lessabsorbing (i.e., does not absorb enough radiation in a single heatingevent to reach the melting temperature of the build material 16), thenthe fusing agent 32 could be applied in one or more of the otherprinting passes. In these instances, the fusing agent 32 could beapplied before or with the electronic agent 30. Also in these instances,the number and conditions of the heating events may be selected so thatthe portion(s) 60, 62 in contact with the fusing agent 32 will fuse uponcompletion of the method. Still further in these instances, passive andactive cooling (e.g., detailing agent 34) may not be used, in partbecause the fusing agent 32 fuses the portion(s) 60, 62 over the courseof the method without absorbing too much radiation.

Still another example of the method is shown in FIGS. 4A through 4D.This example is similar to the example described in reference to FIGS.3E, 3A, 3F and 3G, except that the electronic/fusing agent 30′ alsofunctions as a fusing agent. As such, this example of theelectronic/fusing agent 30′ includes any of the previously describedradiation absorbing binding agents (i.e., active materials).

In this example, the activating agent 36 may be selectively applied tothe portion 70 of the build material layer 58 in a plurality of passesand before the electronic agent 30, the electronic/fusing agent 30′ isselectively applied to the portion 70 in a plurality of passes, thefusing agent 32 is selectively applied to another portion 72 in a singlepass or a plurality of passes, the detailing agent 34 is applied to atleast the portion 72 in a single pass or a plurality of passes, andseveral heating events are performed throughout the passes. The order ofthe passes and heating events is controlled in order to control themechanical property and the conductive property of the fused layer 56′″that is formed. It is to be understood that FIGS. 4A through 4D depictan example of the final printing pass and final heating event to formthe fused layer 56′″.

To control the conductive property, the activating agent 36 and theelectronic/fusing agent 30′ may be applied in several printing passes (2or more), the electronic/fusing agent 30′ may be applied at relativelylow loadings so as to not absorb too much radiation and thus over fusethe build material 16 throughout the process, and the heating events maybe relatively quick so as to not over fuse the build material 16 incontact with the electronic/fusing agent 30′ throughout the process. Tocontrol the mechanical property, a suitable number of heating events areutilized, but the heating events are spread out throughout the printingpasses to avoid over-heating and to manage thermal distribution. Also tocontrol the mechanical property, the detailing agent 34 is utilized forthermal management.

As shown in FIG. 4A, this example method involves applying the buildmaterial 16. The build material 16 may be applied to form a layer 58 aspreviously described.

As an example of this method, one or two heating events may be performedprior to the selective application of any of the agents 30′, 32, 34, 36.This heating event(s) may be performed to preheat the build material 16in the manner previously described.

After preheating, a first printing pass may be performed, during whichat least the activating agent 36 is selectively applied on portion(s) 70of the build material 16 that are to become conductive region(s) 52 inthe fused layer 56′″. The first printing pass may involve theapplication of the activating agent 36 alone, the application of boththe activating agent 36 and the electronic agent 30′, or the applicationof the activating agent 36 and the electronic agent 30′ in portion 70and the detailing agent 34 in portion(s) 72.

After the activating agent 36 is applied to the portion 70 of the buildmaterial 16 (either during printing or to pretreat the build material16), a heating event may be performed. This heating event may be used todry the activating agent 36 before the electronic agent 30′ is applied.This heating event may be active, in that the radiation source 46, 46′is passed over the build material platform 12 or turned on. When thebuild material platform 12 is preheated to an elevated temperature thatcan dry the liquid from the activating agent 36, the heating event maynot be performed prior to the application of the electronic agent 30.

The electronic/fusing agent 30′ may then be dispensed onto the portion70. In this example, when the electronic/fusing agent 30′ is applied onthe portion 70, the nanomaterials 31 can come into contact with thepreviously applied metal salt, which can remove the dispersing agentfrom the nanomaterials 31 and render them more suitable for sintering.

When the activating agent 36 is alone applied in the first pass (whichis associated with a heating event), the second pass may involve theapplication of the electronic/fusing agent 30′ in the portion 70, withor without the application of the detailing agent 34 to actively coolportion(s) 72 of the build material 16 that do not have theelectronic/fusing agent 30′ applied thereto. In this example, the secondpass may be associated with one or two heating events.

When the activating agent 36 and electronic/fusing agent 30′ are appliedtogether in the first pass, the detailing agent 34 may also be applied(during the first pass) to actively cool portion(s) 72 of the buildmaterial 16 that do not have the electronic/fusing agent 30′ appliedthereto. In this example, the first pass may be associated with one ortwo heating events.

When used in the first or second printing pass, the detailing agent 34may provide an evaporative cooling effect that reduces the temperatureof the build material 16 in contact with the detailing agent 34 duringthe heating event(s) following the first printing pass or the secondprinting pass. The use of the detailing agent 34 may eliminate the needfor passive cooling, because the build material 16 exposed to thedetailing agent 34 is maintained at or below the threshold temperatureduring the subsequent heating event(s). Alternatively, passive coolingmay also be used in order to ensure that the build material 16 exposedto the detailing agent 34 is at or below the threshold temperaturebefore the method proceeds with another printing pass.

Moreover, since the electronic/fusing agent 30′ includes a radiationabsorber, the heating events that take place prior to the final heatingevent (e.g., during heating events associated with the first printingpass, second printing pass, etc.) should not completely fuse the buildmaterial 16 in contact with the electronic/fusing agent 30′. This may beaccomplished by shortening the heating events that take place prior tothe final heating event, or applying lower loadings of the electronicagent 30′ in each of the printing passes, or by applying the detailingagent 34 in the portion 70. The total loading of the electronic/fusingagent 30′ applied throughout the method will be suitable to form theconductive region 52, however, the individual loading applied duringeach pass will not allow the build material 16 in portion 70 to fullyfuse until the final heating event is performed.

One or more additional printing passes, during which the activatingagent 36 and the electronic/fusing agent 30′ are selectively dispensedor the activating agent 36, electronic/fusing agent 30′ and thedetailing agent 34 are selectively dispensed, may then be performed, andeach of these additional printing passes may be associated with one ortwo heating events. With any of these additional printing passes, aheating event may follow the application of the activating agent 36 inorder to dry the agent 36.

The plurality of printing passes are used to increase the amount ofactivating agent 36 and electronic/fusing agent 30′ (and thus the amountof the conductive nanomaterials 31 as well as active material) that isapplied to a single layer of build material 16, and in some instances,to apply the detailing agent 34 for thermal management of the portion(s)70, 72 of the build material 16. The plurality of heating events areused to evaporate liquid from the applied activating agent 36, toevaporate liquid from the applied electronic/fusing agent 30′, to heatthe build material 16 or maintain the temperature of the build material16 in the region 72 without fusing/curing the build material 16 (becausethe fusing agent 32 has not yet been dispensed), and/or to begin to fusethe build material 16 in contact with the electronic agent/fusing 30′and to sinter the nanomaterials 31 to form a conductive matrix 31′.

If the detailing agent 34 is not used in the subsequent pass(es) or thebuild material 16 temperature is above the threshold temperature afterthe heating event(s), it is to be understood that the build material 16may be allowed to passively cool to or below the threshold temperatureprior to the next printing pass.

During a final printing pass of this example method, the activatingagent 36 and electronic/fusing agent 30′ are dispensed into the portion70 (as shown in FIGS. 4A-4C); the fusing agent 32 is dispensed on theportion 72 (as shown in FIGS. 4B-4C); and the detailing agent 34 isdispensed on the portion 72 (as shown in FIGS. 4B-4C).

In this example, the activating agent 36 and the electronic/fusing agent30′ are dispensed onto the same portion 70, which has already beenexposed to activating agent 36, electronic/fusing agent 30′, and heatingevents. The portion 70 will form a conductive region 52 of the fusedlayer 56′″. The agents 36, 30′ are capable of penetrating into thespaces between the build material particles 16 in portion 70, as shownin FIG. 4C. Moreover, while not shown, it is to be understood that someof the conductive nanomaterials 31 from the previously dispensedelectronic agent 30′ may already be sintered and some of the buildmaterial 16 in contact with the previously dispensed electronic agent30′ may already be fused when the final printing pass takes place. Inthis instance, the freshly applied activating agent 36 and electronicagent 30′ are capable of penetrating into the spaces between anyremaining unfused build material particles 16 and the conductive matrix31′ that has formed.

In this example, the fusing agent 32 and the detailing agent 34 aredispensed onto the same portion 72. The portion 72 will form anon-conductive or insulating region 54 of the fused layer 56′″. Theamount of fusing agent 32 that is dispensed is enough to absorb adesirable amount of radiation from the subsequently appliedelectromagnetic radiation, and the amount of detailing agent 34 that isdispensed is enough to keep the build material 16 in the portion 72 fromover-heating without preventing fusing. When used in portion 72, it maybe desirable for the detailing agent 34 to contain a colorant thatmatches the color of the fusing agent 32, but does not absorb theapplied electromagnetic radiation.

Both the fusing agent 32 and the detailing agent 34 are capable ofpenetrating into the spaces between the build material particles 16 inportion 72, as shown in FIG. 4C.

While not shown, the detailing agent 34 may be dispensed onto otherportions of the build material 16 that will not be part of the finalfused layer 56′″. These portions do not have electronic agent 30′ orfusing agent 32 thereon, and thus will not fuse. As an example, theseportion(s) may be outside of an edge boundary of the fused layer 56′″.The selective application of the detailing agent 34 in these portion(s)can prevent the build material 16 in these area(s) from fusing and canalso prevent thermal bleed (i.e., heat transferring from the portion 70or 72 which is fused).

Before, during, or after the final pass in which the activating agent36, the electronic/fusing agent 30′, the fusing agent 32, and thedetailing agent 34 are dispensed, all of the build material 16 can beexposed to a final heating event, as shown in FIG. 4D. During thisheating event, the fusing agent 32 facilitates fusing of the buildmaterial particles 16 in contact therewith (i.e., in portion 72) and theelectronic/fusing agent 30′ facilitates fusing of the build materialparticles 16 in contact therewith (i.e., in portion 70) by absorbingenergy from the electromagnetic radiation and converting the energy toheat. The temperature of the build material 16 (in contact with thefusing agent 32 or electronic/fusing agent 30′) is raised above themelting or softening point of the build material 16. As such, the buildmaterial 16 fuses together to form a matrix of fused build material 17.The fused build material 17 at the portion 72 forms the insulatingregion 54 of the fused layer 56′″. At portion 70, the conductivenanomaterials 31 in the electronic/fusing agent 30′ can form additionalconductive matrices 31′ that becomes interlocked with the fused buildmaterial 17. The combination of the fused build material 17 and theconductive matrices 31′ forms the conductive region 52 of the fusedlayer 56′″.

It is to be understood that the various passes and heating eventsdescribed in reference to FIGS. 4A through 4D are performed on a singlelayer 58 of the build material 16 (i.e., prior to the application ofadditional build material 16). After the fused layer 56′″ is formed, anew layer of build material 16 may be applied to the fused layer 56′″and the various passes and heating events may be repeated to formanother fused layer on the fused layer 56′″. These processes may berepeated as many times is desirable to form the final 3D part 50.

In any of the examples disclosed herein, the final part 50 may beexposed to a surface finishing technique, which involves six additionalheating events. It has been found that by exposing the outermost layerof the final part 50 to six additional heating events, the surfacefinish of the final part 50 is aesthetically pleasing and theconductivity of the conductive region(s) 52 are not deleteriouslyaffected. These heating events allow the build material 16 at thesurface of the final part to flow to form a smooth surface. Theseheating events do not deleteriously affect the conductive region(s) (orother electronic region(s)) formed below or at the surface.

Also in any of the examples disclosed herein, the electronic agent 30 orthe electronic/fusing agent 30′ including the material 31 may bedispensed after the fused layer 56, 56′, 56″ is formed. This may bedesirable to form a thin film, conductive, semi-conductive, orinsulating electronic feature between fused layers 56, 56′, 56″.

Any of the examples disclosed herein may be used to form conductiveregion(s) 52 of 3D parts 50. The conductive region 52 can havesufficient electrical conductivity to form electrical components. Theresistance of the conductive region 52 can be tuned in a variety ofways. For example, the resistance can be affected by when and how muchof the active material (in the fusing agent 32 and/or the electronicagent 30′) is dispensed, the number and placement of heating eventsthroughout the process (so that the build material 16 is not overheatedor over fused), the type of metal salt in the activating agent 36, thetype of conductive material in the electronic ink 30, 30′, theconcentration of the conductive material in the electronic ink 30, 30′,the amount of activating agent 36 dispensed, the amount of electronicink 30, 30′ dispensed, the cross section and length of the conductiveregion 52, etc. When the activating agent 36 and the electronic agent30, 30′ is are dispensed by ink jetting, the amount dispensed can beadjusted by changing print speed, drop weight, number of slots fromwhich the agents are fired, and number of passes printed per buildmaterial layer 58. In certain examples, conductive region 52 may have aresistance ranging from about 1 ohm to about 5 Mega ohms.

As mentioned above, sufficient conductivity can be achieved bydispensing a sufficient amount of the conductive material (e.g.,nanomaterial 31) onto the build material 16. In some examples, asufficient mass of the conductive material per volume of the conductiveregion 52 can be used to achieve conductivity. For example, the mass ofconductive material per volume of the conductive region 52 can begreater than 1 mg/cm³, greater than 10 mg/cm³, greater than 50 mg/cm³,or greater than 100 mg/cm³. In a particular example, the mass ofconductive material per volume of the conductive region 52 can begreater than 140 mg/cm³. In further examples, the mass of conductivematerial per volume of the conductive region 52 can be from 1 mg/cm³ to1000 mg/cm³, from 10 mg/cm³ to 1000 mg/cm³, from 50 mg/cm³ to 500mg/cm³, or from 100 mg/cm³ to 500 mg/cm³.

In the examples disclosed herein, the mechanical property may be suchthat the final layer or part exhibits at least 80% of the properties ofthe bulk material. As an example, parts may have a modulus of 1050 MPa.

Still further, the methods disclosed herein may be modified to createelectronic components other than conductive electronic components. Forexample, an electronic agent 30 may be dispensed to create a resistivecomponent. To control a resistive property, the electronic agent 30including the conductive material 31 may be applied at a reducedloading, in a reduced number of printing passes, etc. For anotherexample, an electronic agent 30 may be dispensed to create an insulatingcomponent. To control an insulating property, the electronic agent 30may include an insulating material, and the dispensed loading and/ordrop weight may be controlled to achieve the desirable insulation.

It is to be understood that while several examples of the method havebeen provided herein, the order of the multiple printing passes andmultiple heating events may vary, depending, at least in part, upon theagents 30, 30′, 32, 34, 36 being used. The thermal conditions of thevarious portions 60, 62, 64, 70, 72 may be different throughout themethod (in part because of the different agents that are utilized), andthus different thermal cycles may be used throughout the method. Thethermal cycles may be controlled by the amount of agent 30, 30′, 32, 34,36 utilized, when the agent(s) 30, 30′, 32, 34, 36 are utilized, andwhen heating events are employed in relation to when certain agent(s)30, 30′, 32, 34, 36 are utilized. As described in the various examples,the order of printing passes and heating events may be varied in anysuitable manner in order to achieve a particular mechanical strength ofthe part 50 and a particular conductivity of one or more regions 52 ofthe part 50.

An example of a method 100 for forming three-dimensional (3D) printedelectronic parts is depicted in FIG. 6. It is to be understood that theexample method shown in FIG. 6, variations thereof, etc. are discussedin detail above.

Method 100 includes applying a build material (at reference number 102),and selectively applying an electronic agent in a plurality of passes ona portion of the build material (at reference number 104). A fusingagent is selectively applied on the portion of the build material (atreference number 106). The method 100 further includes exposing thebuild material to radiation in a plurality of heating events, whereinduring at least one of the plurality of heating events, the portion ofthe build material in contact with the fusing agent fuses to form aregion of a layer, and wherein the region of the layer exhibits anelectronic property (at reference number 108).

Method 100 further includes controlling an order of the plurality ofpasses, the selective application of the fusing agent, and the pluralityof heating events to control a mechanical property of the layer and theelectronic property of the region (at reference number 110).

To further illustrate the present disclosure, prophetic comparativeexamples and an example are given herein. It is to be understood thatthese examples are provided for illustrative purposes and are not to beconstrued as limiting the scope of the present disclosure.

EXAMPLES Prophetic Comparative Example 1

A fused layer is prepared with several printing passes and heatingevents.

The materials include: polyamide 12 build material, a sodium chlorideactivating agent (AA), a silver nanoparticle electronic agent (EA), acarbon black fusing agent (FA), and water as a detailing agent (DA). Theconductive regions are to be formed with the AA and the EA and thenon-conductive regions are to be formed with the FA and DA.

The printing system includes 7 ink/fluid channels to dispense theagents, and leading and trailing lamps positioned on either end of thecarriage that accommodates the channels. When printing from right toleft, the leading lamp is exposed to the build material platform priorto the trailing lamp. After the 1^(st) and 3^(rd) printing passes andassociated heating event(s), a controlled cooling step is performed.This involves the printing system waiting until a temperature of thebuild material surface cools down to or below a threshold temperature of142° C. before proceeding with the next printing pass/heating eventsequence.

The printing passes and heating events are set forth in Tables 1 and 2below. N indicates that no agent is printed or that a particular lamp isnot used and Y indicates that the agent is printed or that a particularlamp is used.

TABLE 1 Printing Passes Channel number 1 2 3 4 5 6 7 Agent AA EA EA FADA EA DA Contone level ^(a) 255 120 120 8 8 120 120 Printing pass 1 N NN Y Y N N Printing pass 2 Y Y Y N N Y Y Printing pass 3 Y Y Y Y Y Y YPrinting pass 4 Y Y Y N N Y Y ^(a) Contone level is a parameter tocontrol the ink/fluid density at the image area

TABLE 2 Heating events Leading Lamp Trailing Lamp Heating Events withPrinting pass 1 Y Y Heating Events with Printing pass 2 Y Y HeatingEvents with Printing pass 3 Y Y Heating Events with Printing pass 4 Y N

This example results in an over-fused part. The part is mechanicallystrong and has an aesthetically pleasing surface finish due to thestrong heating conditions, but also has insufficient conductivity in theconductive regions. The conductivity is reduced due to a reduced loadingof the electronic agent (e.g., compared to the maximum loading at 255contone) and to over-fusing, which may result from the fusing agentbeing applied in the first and third printing passes (which enablesenergy absorption during several of the heating events). A typicalresistance of an over-fused part is greater than 850 Ohms.

Prophetic Comparative Example 2

A fused layer is prepared with several printing passes and heatingevents.

The materials include: polyamide 12 build material, a sodium chlorideactivating agent (AA), a silver nanoparticle electronic agent (EA), acarbon black fusing agent (FA), and water as a detailing agent (DA). Theconductive regions are to be formed with the AA and the EA and thenon-conductive regions are to be formed with the FA and DA.

The printing system includes 7 ink/fluid channels to dispense theagents, and leading and trailing lamps positioned on either end of thecarriage that accommodates the channels. When printing from right toleft, leading lamp is exposed to the build material platform prior tothe trailing lamp. After the 1^(st) and 3^(rd) printing passes andassociated heating event(s), a controlled cooling step is performed.This involves the printing system waiting until a temperature of thebuild material surface cools down to or below a threshold temperature of138° C. before proceeding with the next printing pass/heating eventsequence.

The printing passes and heating events are set forth in Tables 3 and 4below. N indicates that no agent is printed or that a particular lamp isnot used and Y indicates that the agent is printed or that a particularlamp is used.

TABLE 3 Printing Passes Channel number 1 2 3 4 5 6 7 Agent AA EA EA FADA EA DA Contone level ^(a) 255 255 255 3 3 255 255 Preheating event N NN N N N N Printing pass 1 Y Y Y N N Y Y Printing pass 2 Y Y Y N N Y YPrinting pass 3 Y Y Y Y Y Y Y ^(a) Contone level is a parameter tocontrol the ink/fluid density at the image area

TABLE 4 Heating events Leading Lamp Trailing Lamp Preheating Event Y YHeating Events with Printing pass 1 Y N Heating Events with Printingpass 2 Y N Heating Events with Printing pass 3 Y N

This example results in an under-fused part. The part is notmechanically strong and does not have an aesthetically pleasing surfacefinish due to the weak heating conditions. The reduction in mechanicalstrength may also be due to the low loading of the fusing agent. Thispart may or may not have adequate conductivity in the conductiveregions. For example, if the temperature is insufficient to fuse theportions with the activating agent and electronic agent, theconductivity may be deleteriously affected.

Example 3

A fused load cell was prepared with several printing passes and heatingevents.

The materials included: polyamide 12 build material, a sodium chlorideactivating agent (AA), a silver nanoparticle electronic agent (EA), acarbon black fusing agent (FA), and water tinted with black dye as adetailing agent (DA).

The load cell was based on the design shown in FIG. 5A. The conductiveregions to be formed with the AA and the EA are shown at referencenumeral 80 and the pad region to be formed with the FA and DA is shownat reference numeral 82.

The printing system included a carriage with 7 ink/fluid channels todispense the agents. Leading and trailing lamps were positioned oneither end of the carriage, and these lamps were used for the heatingevents as shown in Table 6. The carriage speed during preheating was 20inches per second (ips). The carriage speed during printing was 20 ipsfor each of the passes (see Table 5) per printed layer. A 50 millisecondwait time was utilized after each carriage pass/heating event wasperformed to allow for passive cooling. The temperature set point forthe supply-side of the printer (i.e., the carriage) was 90° C.

Fourteen (14) layers of the polyamide 12 build material were spread andheated before printing was initiated. The build material platform wasmaintained at 150° C., but a temperature drop was observed after thefirst 10 layers were preheated. The build material platform temperaturewas 132° C. for the 11^(th) layer, 131° C. for the 12^(th) layer, 130°C. for the 13^(th) layer, and 129° C. for the 14^(th) layer. A 15^(th)layer was applied and preheated with the build material platformtemperature at 129° C. This temperature then remained constantthroughout printing. Layer 15 was the first layer upon which printingtook place. A total of 52 layers were printed (including layer 15).

The printing passes and heating events are set forth in Tables 5 and 6below. N indicates that no agent was printed or that a particular lampwas not used and Y indicates that the agent was printed or that aparticular lamp was used.

TABLE 5 Printing Passes Channel number 1 2 3 4 5 6 7 Agent AA EA EA FADA EA DA Contone level ^(a) 255 255 255 8 or 6 8 or 6 255 64 or 96 or 4or 4 Preheating events N N N N N N N Printing pass 1 Y Y Y N N Y YPrinting pass 2 Y Y Y N N Y Y Printing pass 3 Y Y Y Y Y Y Y ^(a) Contonelevel is a parameter to control the ink/fluid density at the image area

TABLE 6 Heating events Leading Lamp Trailing Lamp Preheating Events Y YHeating Events with Printing pass 1 Y N Heating Events with Printingpass 2 Y Y Heating Events with Printing pass 3 Y N

This example resulted in the fused load cell shown in FIG. 5B. The partwas mechanically strong, and had a modulus of 1050 MPa. As depicted, thepart also had an aesthetically pleasing surface finish.

The fused load cell also had conductive regions, which can be seen inthe X-ray of the fused load cell in FIG. 5C. The X-ray clearlyillustrates the internal wiring that was formed. The resistance of eachof the four conductive regions was below 200 ohms (e.g., ranging from128 ohms to 193 ohms). The desirable conductivity was achieved, in part,by using the maximum loading of the AA and the EA, by printing theseagents several times, and by spacing the heating events throughout theprinting passes so that over-fusing did not occur.

The fused load cell was not over-fused due, at least in part, to the FAbeing printed only in the last pass, the DA being printed to preventover-heating, and the use of passive cooling between printing/heatingsequences.

It is to be understood that while prophetic examples 1 and 2 and example3 illustrate the use of four carriage passes (including heating event(s)and/or printing passes), more carriage passes with heating event(s)and/or printing passes may be utilized to create parts with suitableelectronic and mechanical properties.

Reference throughout the specification to “one example”, “anotherexample”, “an example”, and so forth, means that a particular element(e.g., feature, structure, and/or characteristic) described inconnection with the example is included in at least one exampledescribed herein, and may or may not be present in other examples. Inaddition, it is to be understood that the described elements for anyexample may be combined in any suitable manner in the various examplesunless the context clearly dictates otherwise.

It is to be understood that the ranges provided herein include thestated range and any value or sub-range within the stated range. Forexample, a range from about 50 μm to about 300 μm should be interpretedto include the explicitly recited limits of about 50 μm to about 300 μm,as well as individual values, such as 55 μm, 125 μm, 130.5 μm, etc., andsub-ranges, such as from about 65 μm to about 225 μm, etc. Furthermore,when “about” is utilized to describe a value, this is meant to encompassminor variations (up to +/−10%) from the stated value.

In describing and claiming the examples disclosed herein, the singularforms “a”, “an”, and “the” include plural referents unless the contextclearly dictates otherwise.

While several examples have been described in detail, it is to beunderstood that the disclosed examples may be modified. Therefore, theforegoing description is to be considered non-limiting.

What is claimed is:
 1. A method for forming three-dimensional (3D)printed electronic parts, the method comprising: applying a buildmaterial; selectively applying an electronic agent in a plurality ofpasses on a portion of the build material; selectively applying a fusingagent on the portion of the build material; exposing the build materialto radiation in a plurality of heating events; wherein: during at leastone of the plurality of heating events, the portion of the buildmaterial in contact with the fusing agent fuses to form a region of alayer; and the region of the layer exhibits an electronic property; andcontrolling an order of the plurality of passes, the selectiveapplication of the fusing agent, and the plurality of heating events tocontrol a mechanical property of the layer and the electronic propertyof the region.
 2. The method as defined in claim 1 wherein: the portionof the build material is less than all of the build material; the methodfurther comprises: selectively applying the fusing agent on an otherportion of the build material; and selectively applying a detailingagent on the other portion of the build material; during at least one ofthe plurality of heating events, the other portion of the build materialin contact with the fusing agent fuses to form a remaining region of thelayer; and; the detailing agent controls a maximum temperature at whichthe other portion of the build material fuses.
 3. The method as definedin claim 1 wherein: the portion of the build material is less than allof the build material; the method further comprises selectively applyinga detailing agent on an other portion of the build material; thedetailing agent controls a maximum temperature that the other portion ofthe build material achieves; and the other portion of the build materialin contact with the detailing agent does not fuse.
 4. The method asdefined in claim 1 wherein the selectively applying of the electronicagent in the plurality of passes, the selectively applying of the fusingagent, and the exposing of the build material to radiation in theplurality of heating events occur prior to an application of additionalbuild material.
 5. The method as defined in claim 1, further comprisingselectively applying an activating agent in a plurality of passes on theportion of the build material, wherein the activating agent includes achloride salt, a bromide salt, or an iodide salt.
 6. The method asdefined in claim 1, further comprising cooling the build material to athreshold temperature after at least one of the plurality of heatingevents and prior to at least one other of the plurality of heatingevents.
 7. The method as defined in claim 6 wherein the build materialis a polymeric build material, a ceramic build material, a metallicbuild material, or a composite build material, and the thresholdtemperature ranges from about 10° C. to about 100° C. below a meltingpoint the build material.
 8. The method as defined in claim 2 whereineach of the selectively applying of the electronic agent, theselectively applying of the fusing agent, and the selectively applyingof the detailing agent is accomplished in at least one printing pass bythermal inkjet printing, piezoelectric inkjet printing, or continuousinkjet printing.
 9. The method as defined in claim 8 wherein: at leastone of the plurality of heating events is accomplished prior to at leastone of the selectively applying of the electronic agent or theselectively applying of the fusing agent; and at least one other of theplurality of heating event is accomplished subsequent to the at leastone printing pass.
 10. The method as defined in claim 2 wherein thedetailing agent is tinted with a colorant.
 11. The method as defined inclaim 1 wherein the electronic agent includes metal nanoparticles, acarbon conductor, a conductive polymer, or a metal organic decompositionsalt.
 12. A method for forming three-dimensional (3D) printed electronicparts, the method comprising: applying a build material; selectivelyapplying an electronic agent in a plurality of passes on a portion ofthe build material; selectively applying an activating agent in aplurality of passes on the portion of the build material; exposing thebuild material to radiation in a plurality of heating events; wherein:during at least one of the plurality of heating events, the portion ofthe build material in contact with the electronic agent and theactivating agent fuses to form a region of a layer; and the region ofthe layer is exhibits an electronic property; and controlling an orderof each of the plurality of passes and the plurality of heating eventsto control a mechanical property of the layer and the electronicproperty of the region.
 13. The method as defined in claim 12 wherein:the portion of the build material is less than all of the buildmaterial; the method further comprises: selectively applying a fusingagent on an other portion of the build material; and selectivelyapplying a detailing agent on the other portion of the build material;during at least one of the plurality of heating events, the otherportion of the build material in contact with the fusing agent fuses toform a remaining region of the layer; and; the detailing agent controlsa maximum temperature at which the other portion of the build materialfuses.
 14. The method as defined in claim 12 wherein the activatingagent includes a chloride salt, a bromide salt, or an iodide salt.
 15. Athree-dimensional (3D) printing system, comprising: a supply of buildmaterial; a build material distributor; a supply of an electronic agent;a first applicator for selectively dispensing the electronic agent; asupply of an activating agent; a second applicator for selectivelydispensing the activating agent; a supply of a fusing agent; a thirdapplicator for selectively dispensing the fusing agent; a supply of adetailing agent; a fourth applicator for selectively dispensing thedetailing agent; at least one fusing lamp; a controller; and anon-transitory computer readable medium having stored thereon computerexecutable instructions to cause the controller to: utilize the buildmaterial distributor to dispense the build material; utilize the firstapplicator and the second applicator to respectively and selectivelydispense in a plurality of passes the electronic agent and theactivating agent; utilize the third applicator and the fourth applicatorto respectively and selectively dispense the fusing agent and thedetailing agent; and utilize the at least one fusing lamp to expose thebuild material to radiation in a plurality of heating events to form athree-dimensional part having an electronic property.